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烟草产业英文作文英文：The tobacco industry has always been a controversial topic. On one hand, it provides jobs and generates revenue for the economy. On the other hand, it is a leading cause of preventable diseases and death. As a result, theindustry has been heavily regulated and taxed in many countries.In my opinion, the tobacco industry has both positive and negative impacts. On the positive side, it creates jobs for farmers, factory workers, and salespeople. For example, in China, where I am from, tobacco farming provides income for many rural families. In addition, the industry contributes to government tax revenue, which can be usedfor public services such as healthcare and education.However, the negative effects of the tobacco industry cannot be ignored. Smoking has been linked to varioushealth problems, such as lung cancer, heart disease, and respiratory issues. As a result, healthcare costs have increased, and many families have been affected by the loss of loved ones due to smoking-related illnesses.中文：烟草产业一直是一个备受争议的话题。
烟草英文文案作文素材英文回答：Tobacco's Devastating Impact on Health。
Tobacco use is a leading cause of preventable death and disease worldwide. According to the World Health Organization (WHO), tobacco kills more than 8 million people annually. The vast majority of these deaths are due to non-communicable diseases such as cancer, cardiovascular disease, and chronic respiratory diseases.Cancer。
Tobacco smoke contains over 7,000 chemicals, many of which are known carcinogens. These chemicals damage the DNA in cells, leading to uncontrolled cell growth and the development of cancer. Tobacco use is the leading cause of lung cancer, but it can also cause cancer of the mouth, throat, larynx, esophagus, stomach, pancreas, kidney,cervix, and leukemia.Cardiovascular Disease。
Tobacco smoke damages the blood vessels and heart. It increases the risk of heart attack, stroke, and peripheral artery disease. Tobacco use also contributes to high blood pressure, which is a major risk factor for cardiovascular disease.Chronic Respiratory Diseases。
烟草运动英语作文高中英文回答：From the moment of its inception, the anti-tobacco movement has faced an uphill battle. The tobacco industry, with its deep pockets and powerful influence, has spared no expense in countering efforts to reduce smoking rates. Despite the challenges, the movement has made significant strides in raising awareness about the dangers of tobacco use and advocating for policies to protect the public from its harmful effects.The movement's early roots can be traced back to the 1950s, when a series of studies established a causal link between smoking and lung cancer. These findings ignited a public outcry, leading to the formation of organizations such as the American Cancer Society and the American Lung Association. These groups played a pivotal role in educating the public about the risks of tobacco use, dispelling the industry's claims that smoking was harmless.In the 1960s and 1970s, the movement gained momentum with the passage of a series of landmark laws, including the Public Health Cigarette Smoking Act of 1969, which banned cigarette advertising from television and radio. These measures helped to reduce smoking rates, particularly among young people.However, the tobacco industry fought back with a sophisticated campaign of misinformation and lobbying. They funded research to cast doubt on the link between smoking and disease, and they spent millions of dollars on marketing to entice new smokers. The industry also targeted young people, promoting smoking as a symbol of rebellion and independence.Despite these setbacks, the movement continued to make progress. In 1998, the Master Settlement Agreement was reached between the tobacco industry and 46 states. This agreement imposed billions of dollars in fines on the industry and required them to fund anti-smoking campaigns.The settlement also gave states the authority to regulate tobacco sales and marketing.In recent years, the movement has embraced new strategies to address the evolving tobacco landscape. E-cigarettes and other nicotine delivery systems have emerged as a new challenge, and the movement has advocated for policies to prevent their use by young people. Additionally, the movement has focused on reducing disparities in smoking rates among minority and low-income populations.The anti-tobacco movement has faced numerous challenges over the years, but it has persevered, driven by a deep commitment to public health. The movement has saved countless lives, and its work continues to be vital in protecting future generations from the devastating effects of tobacco use.中文回答：自诞生之日起，反烟草运动就面临着艰巨的挑战。
烟草产业的英文作文英文：Tobacco industry has been a topic of controversy for years. As a smoker, I have mixed feelings about it. On one hand, I enjoy smoking and find it relaxing. On the other hand, I am aware of the health risks associated with it and the negative impact it has on the environment.From an economic standpoint, tobacco industry is a major contributor to many countries' GDP. It provides jobs for millions of people and generates billions of dollars in revenue. However, the cost of treating smoking-related illnesses puts a strain on healthcare systems and can have a negative impact on a country's economy in the long run.From a health perspective, smoking is a major cause of preventable deaths worldwide. It increases the risk of lung cancer, heart disease, stroke, and other serious health problems. Despite the warning labels on cigarette packs andpublic health campaigns, many people still choose to smoke.From an environmental perspective, tobacco farming requires a significant amount of water and pesticides, which can have a detrimental effect on the environment. Cigarette butts are also a major source of litter and can take years to decompose.In conclusion, while tobacco industry has its benefits, it also has its drawbacks. As a smoker, I am aware of the risks associated with smoking and try to be responsible by disposing of my cigarette butts properly. As a society, we need to continue to educate people about the dangers of smoking and work towards finding alternative sources of revenue.中文：烟草产业多年来一直是一个争议的话题。
烟草运动英语作文初中The Tobacco Control Movement。
The tobacco control movement, also known as the anti-smoking movement, is a global effort to reduce the consumption of tobacco and to protect people from the harmful effects of tobacco smoke. It aims to raise awareness about the dangers of smoking and to promote policies that discourage smoking and support those who want to quit.In recent years, the tobacco control movement has gained significant momentum worldwide. Governments, public health organizations, and individuals have joined forces to combat the tobacco epidemic. One of the key strategies employed by the movement is to educate the public about the health risks associated with smoking. Through various campaigns, advertisements, and educational programs, people are made aware of the link between smoking and diseases such as lung cancer, heart disease, and respiratoryproblems.Another important aspect of the tobacco control movement is the implementation of policies and regulations to reduce smoking rates. Many countries have introduced measures such as higher taxes on tobacco products, graphic warning labels on cigarette packages, and restrictions on smoking in public places. These policies aim to make smoking less affordable, less socially acceptable, and less accessible, thereby discouraging people from starting and encouraging smokers to quit.Moreover, the tobacco control movement provides support and resources for those who want to quit smoking. Quit lines, counseling services, and nicotine replacement therapies are made available to help smokers overcome their addiction. Additionally, support groups and online communities offer a platform for smokers to share their experiences, seek advice, and find encouragement from others who are also trying to quit.The tobacco control movement has achieved significantsuccesses in reducing smoking rates and protecting public health. In countries where comprehensive tobacco control measures have been implemented, smoking rates have declined, and the number of tobacco-related deaths and diseases has decreased. However, challenges remain. The tobacco industry continues to use aggressive marketing tactics to target young people and vulnerable populations. Additionally, the rise of alternative tobacco products such as e-cigarettes poses new challenges to tobacco control efforts.In conclusion, the tobacco control movement plays a crucial role in reducing tobacco consumption and protecting public health. Through education, policy implementation,and support services, the movement aims to create a smoke-free world. While progress has been made, continued efforts are needed to overcome the challenges posed by the tobacco industry and emerging tobacco products. By working together, we can create a healthier future for generations to come.。
烟草产业的英文作文英文：Tobacco industry has always been a controversial topic. As a virtual assistant, I do not have personal opinions, but I can provide some facts and figures.Firstly, tobacco is a highly profitable industry. According to the World Health Organization (WHO), the global tobacco market was worth $888 billion in 2018. However, this industry also brings about negative impacts, such as health problems caused by smoking, environmental pollution from tobacco cultivation, and social issues like addiction and crime.Secondly, the tobacco industry provides employment opportunities for millions of people worldwide, especially in developing countries where tobacco is a major export. For instance, in Zimbabwe, tobacco accounts for over 60% of the country's agricultural exports and employs around150,000 farmers. However, the working conditions and wages of tobacco workers are often poor, and child labor is prevalent in some countries.Thirdly, the tobacco industry has a significant influence on politics and society. Tobacco companies spend billions of dollars on lobbying and advertising to promote their products and protect their interests. This can lead to conflicts of interest with government policies aimed at reducing smoking rates and protecting public health.In conclusion, the tobacco industry is a complex and multifaceted issue. While it brings economic benefits to some regions, it also poses risks to public health and the environment. As individuals, we should be aware of the consequences of smoking and support policies that aim to reduce tobacco consumption.中文：烟草产业一直是一个有争议的话题。
烟草产业的英文作文The tobacco industry is a controversial and complex business. It has been a major player in the global economy for centuries, providing jobs and revenue for many countries. However, it also has a dark side, as tobacco products are known to cause serious health issues and addiction.Tobacco cultivation requires specific climate and soil conditions, making it a challenging crop to grow. The industry also involves extensive processing and manufacturing to produce various tobacco products, such as cigarettes, cigars, and chewing tobacco.The marketing and advertising tactics used by the tobacco industry have been a source of controversy for many years. They have been accused of targeting vulnerable populations, such as young people and low-income communities, in their efforts to promote their products.The health risks associated with tobacco use are well-documented. Smoking is a leading cause of preventable death worldwide, contributing to a wide range of health problems, including cancer, heart disease, and respiratory issues. Despite these risks, the demand for tobacco productsremains high in many parts of the world.The tobacco industry has faced increasing regulationand public scrutiny in recent years. Many countries have implemented strict laws and policies to control tobacco use and reduce its negative impact on public health. These efforts have included measures such as higher taxes on tobacco products, restrictions on advertising, and public smoking bans.In conclusion, the tobacco industry is a complex and multifaceted business with both positive and negative impacts. While it has been a significant economic force for many countries, it also poses serious health risks and ethical concerns. As society continues to grapple with the challenges posed by tobacco use, the industry is likely to face continued scrutiny and regulation in the years to come.。
专四听写tobacco is the leadingTobacco smoke kills thousands of people every year and hurts hundreds of thousands of people like children every day. Federal officials released a massive report that sparked new efforts to ban smoking in public places. Secondhand smoke has been classified as a known carcinogen and this classification is shared by ten other pollutants.(These pollutants include benzene, asbestos, and smoke inhaled directly from cigarettes. Governor Mario Cuomo) asked the legislature to ban smoking on campus, and anti-smoking advocates said they would target chains of similar bans on airlines and fast-food restaurants.The risk of developing lung cancer due to tobacco smoke is1in1,000for no nsmokers and2in1,000for nonsmoking spouses of smokers.However,the risk f or smokers is70in every1,000.Passive smoking causes between150,000and300,000cases of bronchitis,pn eumoia and similar infections in children less than18months old and worsens th e condition of between200,000and1million asthmatic children.It is pointless to allow people to smoke in one part of a restaurant and not to allow it in another w hen eventuallly the nonsmoking section breathes in the smoke.In conclusion,second hand smoke is a human carcinogen that kills about3,0 00U.S.nonsmokers because of lung cancer annually.Annual reasons for lung cancer and not for smokers. Cigarette smoke causes between 150,000 to 300,000 cases of bronchitis and pneumonia in children with other lower respiratory tract infections younger than 18 months old. Tobacco smoke is known to cause an effusion in the middle ear, causing a variety of infections. As has been seen, smoking is not recommended in public because it has effects on both smokers and non-smokers.。
Tobacco should be treated as illegal like other drugs. Smoking has not a single positive issue but lots of negative effects and therefore, it should be banned.To what extent do you agree or disagree with the above statement. Give reasons for your answer and include any relevant examples from your experience. You should write at least 250 words.Model Answer 1 :The drugs those are strong and cause harm to human are considered illegal and are prohibited in almost all the countries considering the bad effects. Those drugs are very much addictedand the people who take it regularly destroy his life and can not lead a normal life. Likewise, tobacco is another phenomenon that has a strong beckoning towards people of all ages. Considering the bad effects, therefore, it should be considered unlawful and prohibited.There are lots of substances presented in the tobacco and people become much more addictive to the tobacco because it is easily accessible and does not cost that much at a time compared to other illegal drugs. There are enough scientific reasons to believe that once a person becomes addicted towards tobacco,can't leave it easily like other strong drugs. Many people even exhaust more than 20 cigarettes daily and eventually increase the possibility to be infected with lung cancer or many other serious diseases. The person who smokes or takes tobacco in other ways harms himself as well as the people surrounding them. Because it is proven in medical science that second-hand smoking causes the same physical problems as the first-hand smoking does. So considering the issue I strongly opine that all tobacco should be banned like other harmful drugs. Many people think that tobacco creates some opportunities. For instance, they mention the number of peopleinvolved in these industries from farmer to manufacturing workers. They also think that tobacco companies often help people by sponsoring big sports events, initiating some social works like tree-plantation, star search programs etc.In my opinion, all those are eye wash for people. The companies are uplifting their fortunes by destroying innocent peoples' lives. Think about a family that has loose their only earning member because he was a chain smoker for 20 years and recently died of lung cancer. The effects are overwhelming compared to what tobaccocompanies do for us. I believe there are lots of organisations who are happy to initiate the same social programs for the betterment of people. Science has proven that the amount of nicotine contained in a cigarette is pushed directly into someone's body, he will die at once. So tobacco business is a social crime at large.Furthermore, those who cultivate tobacco, process it prepare cigarette and smokes ultimately become the victims of many serious diseases like cancer, heart diseases and bronchitis. In addition buying tobacco costs money which could have been used for somegood thing. Teenagers addicted to tobacco involve themselves to some other drugs and tobacco is always the gateway to other drugs. I don't think there is any one benefit we get from tobacco rather it harms us in so many ways. There are huge scarcities of food in the world right now and a huge amount of fields and many farmers are engaged in producing tobacco.So I strongly give my opinion to declare the cultivation, production, manufacturing and selling of tobacco should be strictly prohibited for all our betterment.Model Answer 2:Health is considered the most precious gift that we all have so it is essential to think carefully about things that may have a harmful effect on individuals. Many people argue that tobacco smoking should be considered illegal as other drugs because it has more detriments than benefits. However, this is refuted by others. Both sides will be critiqued before a reasoned conclusion is formed.It is felt by many that cigarette smoking has deleterious effects on person's life. For example, it has been shown in many research studies that tobacco is one of the risk factors to manydiseases including cancer, particularly lung cancer, cardiovascular diseases and others. This example clearly shows that smoking can be very harmful and has a tremendous financial burden on not only the personal budget but also health sector. On the other side, many people think that smoking is a personal decision.In addition, it cannot be compared to drugs as it provides health benefits like memory and attention enhancing and preventing ulcerative colitis. Moreover, it is used in some medications.After analysing these two points of view, I believe that the cons of smoking outweigh thepros and the usage of tobacco should be limited for medical treatments authorised by governments. Without a doubt, I think that smoking is an important topic that has effects on various aspects of human's life and other people's life as no one focus on the passive smoking issue and the government should pay more attention and invent new policies regarding smoking.Sample Essay 3:Most of the drugs are banned in all nations as they are the root cause of many incurable diseases, mental instability and social problems.Tobacco is considered similar to these drugs, as it engenders a myriad of negative impacts on the human beings. I totally agree that tobacco must be banned as it can engender diseases as well as can cause addictions.Firstly, it is apparent that smoking can lead to vulnerable diseases like cancer, as tobacco contains a harmful ingredient called Nicotine. Moreover, smoking not only creates a physical imbalance among the smokers but also attracts diseases among passive smokers due to the air pollution created by it. A research done, in August 2014 by a group of scientists based inCalifornia, illustrates that seventy percent of the people affected by smoking are non-smokers. Therefore, it is crystal clear that Nicotine must be prohibited. Secondly, almost all smokers are addicted to the smoking habit, due to the reason that Nicotine attracts this peculiar characteristic.Furthermore, if a smoker forcefully tries to put an end to the smoking habit, it is predicted that he or she will come under mental imbalance. For instance, if a patient asks some remedies with a physician to give up smoking, definitely the doctor would recommend decreasing the habit on a daily basis, instead of stopping suddenly. Itmight take a few years to get rid of this habit. Thus, it is obvious that tobacco has a huge negative impact. Smoking does not have a single positive side and tha t’s why it should be immediately banned. It costs a large amount of money, it puts our mental and physical health in danger and creates many others diseases to people.In conclusion, by analysing how tobacco can destroy the health of people as well as cause addiction, it is obvious that Tobacco products must be banned. It is suggested that governments give banning notice well inadvance so that the smokers can quit the habit slowly.。
Version 00106范文1Nowhere in the world has the issue of tobacco been so much debated as inour society. Nowadays, tobacco is more harmful than drug to people’s health, therefore many people think that smoking is legal that is a direct andprimary reason to induce this kind of problem. The above point is certainlytrue; this essay will outline three reasons.The main reason is that tobacco is a silent killer to smokers. Tobacco is known to be the probable cause of some 25 different diseases, and for some,such as lung cancer, bronchitis and emphysema, it is the main cause. According to a WHO report four million people die yearly from tobacco-related diseases, that is one death every eight seconds. Tobacco is significantly becoming a greater cause of death and disability than any other single cause.Another reason is that more and more young people are under 18 years old who smoke cigarette have been blinded by the deceit of tobacconists. Tobacco among adolescents remains stubbornly persistent. Smoking among adolescents rose in the 1990s in several developed countries，such as China,Vietnam and Thailand . While new markets are being opened by the tobacco industry actions, old markets have not been closed. Tobacco is a global threat.Last but not the least reason is the increase in cigarette smuggling. Becauseof tobacco smuggling, the legal retailing and distribution systems are badlyaffected, and faced with increased lawlessness and heavy tax losses. This behavior severely affects the economy.In conclusion, the tobacco should be considered illegal. Perhaps a packofcigarettes is less harmful than another drug, but tobacco is actually the biggest killer of all the drugs.================================================= 范文2Advertisements of tobacco and those of “smoking is harmful”are often seentogether. But there has been an on-going argument about whether or not tobacco should be forbidden and made illegal. I have always believed that smoking should be illegal for the following reasons.First, smoking does great harm to human health and causes many diseases. It is reported that more than 70% of lung cancer sufferers are smokers, andthe average life-span of smokers is seven years less than that of non- smokers. Moreover, it hurts not only smokers, but also the ones around thesmokers. Many researchers claim that breathing “second-hand smoke”maybe even more harmful than smoking.Second, many social problems and disasters can be attributed to smoking. For instance, many wives cannot bear their husbands’ smoking all the time, which causes many quarrels, or even divorces. Furthermore, the biggest firedisaster in China, the Daxinganling fire disaster, was caused by a burning cigarette end, and the cost of the resulting loss was unimaginable.Last, smoking tobaccos is a main source of air pollution.A magazine said thatfor every cigarette smoked each day,a whole tree is needed to clean the air.In other words, smoking one less cigar every day equals planting a tree. It is a brilliant contribution to the earth we are living on.In a word, all the above demonstrate that smoking harms yourselves as wellas your neighbors, pollutes the air we ourselves are breathing, and even agitates the social peace. So, in my opinion, tobacco should be strictly forbidden, and smoking should be made illegal.范文3there has long been controversy over the legality and apparent acceptance of tobacco in society .some hold that cigarettes and other tobacco containing products should be banned, that is, treated asnarcotics.personally,i agree with this point of view for the following reasons:although cigarettes do not offer as intense an effect as drugs like heroin and cocaine,they rank higher in the level of dependence it creates in the user.thousands of smokers try to rid themselves of cigarettes but cannot,because of the physiological dependence they developed,chiefly imputable to its chemical nicotine.this explains why smokers continue their habit despite the numerous health warnings. furthermore,medical science has now proved beyond a doubt that smoking kills.with all the other causes of preventable deaths such as alcohol,illegaldrugs,aids,suicide,road accidents,fire,and guns,cigarettes still account for more preventable deaths than all of those combined.more disturbingly,whilst the use of heroin is dangerous solely to the users,the use of tobacco endangers those who are in their vicinity as well. this phenomenon, known as passive smoking, nulls the counter-argument that putting one's own health at risk through smoking should be up to one's own individual choice.reports have shown that the amount of second-hand smoke inhaled by a typical nonsmoker is equivalent to one cigarette smoked per day,and what is more,passive smoking can increase a nonsmoker's chance of getting cancer by ten to thirty two per cent. there are those who will say that the black market created by outlawing tobacco will produce deadlier cigarettes because the product standards of the bootleggers are not as high.however,we should all bear in mind that legal cigarettes cause roughly four hundred thousand deaths a year.it is hard to imagine the limited distribution provided by the criminal underworld could compete with this tragic figure.to sum up, the harm visited upon our society by tobacco usage is substantial.there will be no solution other than to control tobacco much in the same way that the government now controls drugs which could allow people to remain attentive to the seriousness of the effects of these substances,and hopefully to prohibit their usage.范文4Apparently, it would seem that tobacco is totally different substance from drugs, and it can be used freedom by public. In fact, however, our authority should make tobacco illegal as well as drugs, and using of tobacco should be controlled strictly.Tobacco only can be used for research and medical purpose. As far as I am concerned, as a kind of dope, tobacco has been widely used to help patients alleviate their pain in surgery. At the same time, ordinary people should not be allowed to access it legally for two main reasons.Among countless factors which influence my inclination, there is a most conspicuous one: it is harmful that smokers addict to tobacco. Many decades ago, scientists have already found that there is a definite link between smoking and bronchial troubles, cardiac disease and lung cancer. More seriously, it not only has negative influence for smokers, but others living or working in same surrounding, even the next generation of a smoking pregnant women may be harmed by so-called “second hand smoking”. Research shows that sometimes “second hand smoking” is more dangerous than smoking directly, because, at least smokers can get the protection from filter tips to some extent. Thus, compared to the hazard of drugs, tobacco can involve more other innocent people and harm their health unknowingly.The second aspect relates to the problem that our natural resources and money are wasted senselessly during the course of planting, transporting and manufacturing tobacco. In light of a statistics, China consumes nearly 1,000 tons of wood fibers to produce cigarettes annually. Besides, the investment absorbed by tobacco manufacturers every year, is enough to solve all financial troubles that higher education have to face. Obviously, if tobacco is banned by our governments, it means that considerable money will be saved.In summary, judging from all the evidence offered, we may safely arrive at the conclusion that tobacco should be forbidden as well as drugs except for a few special purposes, such as research and medicine.补充With the development of society, our life and working pressure are greater and greater. In this way, a lot of people have become smokers. Tobacco, as a kind of drugs, prevails in the society. Some people hold the opinion that tobacco should be given freedom be use, but others, in contrast, deem it should be made illegal as the same way as other drugs and that is also my point.Medical science proves that smoking can cause the heart diseases, lung cancer, and the immune system diseases. These diseases are all mankind's healthy enemies. The statistics have showed that people who die of the lung cancer, over 90% are smokers. In these smokers, 85% are chain smoker. So, obviously, there is enormous danger to the human health in smoking.In addition, smoking not only dangerous to smoker, but also do harm to people at smoker's side. The tobacco contains a large number of noxious substances, such as nicotine. Just as a famous physician says, smoking is equivalent to commit suicide chronically.However, the cigarette can really relax our nervous nerve, within short time. People, especially, who have heavy working pressure, are prone to produce sense of relying on to cigarette. Moreover, as everyone knows, a lot of countries impose the heavy taxation to tobacco manufacturer and seller, thus, if the tobacco business is considered as the illegal activities, the revenues of the country will be reduced correspondingly.In a word, the danger to people of cigarette is obvious. Though it can help us flee away from pressure, this to use health as cost. Our government should forbid the production of the tobacco, make our world fresh and nonpoisonous.With the development of society, our life and working pressure are [getting] greater and greater.In this way, a lot of people have become smokers. Tobacco, as a kind of drugs, prevails in the society. Some people hold the opinion that tobacco should be given freedom [to] be [used, but others, in contrast, deem [that] it should be made [as] illegal as the same way as other drugs and that is also my point.Medical science proves that smoking can cause the heart diseases, lung cancer, and the immune system diseases. [all of these diseases are enemies of mankind's healthy] . The statistics have showed that people who die of the lung cancer, over 90%, are smokers. [Among] these smokers, 85% are chain smokers. So, obviously, there is enormous danger to the human health in smoking.In addition, smoking not only dangerous to smokers, but also [does] harm to people atsmoker's side. The tobacco contains a large number of noxious substances, such as nicotine. Just as a famous physician says, smoking is equivalent to commit suicide chronically. However, the cigarette can really relax our nervous nerve, within short time. People, especially, who have heavy working pressure, are prone to produce sense of relying on to cigarette. Moreover, as everyone knows, a lot of countries impose the heavy taxation to tobacco manufacturer and seller, thus, if the tobacco business is considered as the illegal activities, the revenues of the country will be reduced correspondingly.To sum up, the danger to people of cigarette is obvious. Though it can help us flee awayfrom pressure, this to use health as cost. Our government should forbid the production ofthe tobacco, make our world fresh and nonpoisonous.Although it is a freedom to use tobacco{烟草} while some people think it should be made illegal as the same way as other drugs. To what extent do you agree or disagree？ What’s your opinion?A:Tobacco should be made illegal, I agree with this idea personally. I hope most drugs can be made illegal, because, as far as I know, they are bad to our health. However, currently most countries still keep it free to use tobacco, and this situation seems to be very hard to change in a short time.From my own experience, using tobacco is not a good thing, especially using is for a long time. It will lead to many kinds of diseases, more importantly, many of them are fatale. One of my friends died from using too much tobacco, and it is believed there are many more people like this. The other thing that I am concerned of is, if a country doesn’t make using tobacco illegal, many young people will have a chance to use it, i.e. students. It is very dangerous, because if someone gets addicted to this when he is very young, he will thenalmost surely have a big health problem when he is old.I am happy to see that, although it is free to use tobacco in many countries, most of those countries still somehow try not to encourage people using it. For example, tobacco advertisement is banned in many countries, and for many countries, smoking is banned in public places. Overall, most countries are trying to stop the use of tobacco, though it will take sometime. In my opinion, it is essential to limit the use of tobacco, and I hope everyone doesn’t use.。
i n d u s t r i a l c r o p s a n d p r o d u c t s28(2008)294–302Tobacco stems as a low cost adsorbent for the removal ofPb(II)from wastewater:Equilibrium and kinetic studiesWei Li a,b,Libo Zhang a,Jinhui Peng a,∗,Ning Li a,Shimin Zhang a,Shenghui Guo aa Faculty of Materials and Metallurgical Engineering,Kunming University of Science and Technology,Kunming650093,PR Chinab Faculty of Science,Kunming University of Science and Technology,Kunming650093,PR Chinaa r t i c l e i n f oArticle history:Received5December2007Received in revised form17February2008Accepted22March2008Keywords:Tobacco stemsAdsorptionLead ions(II)IsothermKineticsa b s t r a c tAdsorption of Pb(II)ions from aqueous solution onto tobacco stems has been investigated toevaluate the effects of initial lead ion concentration,adsorbent dosage,contact time,pH andtemperature on the removal of Pb(II)systematically.The optimal pH value for Pb(II)adsorp-tion onto the tobacco stems was found to be5.0.The removal of lead ions for concentrations10,30and50mg L−1using0.8g adsorbent at contact time of120min and at temperature of299K were94.37%,92.10%and90.43%,respectively.Thermodynamic parameters such asstandard Gibbs free energy( G◦),standard enthalpy( H◦),and standard entropy( S◦)wereevaluated by applying the Van’t Hoff equation,which describes the dependence of equilib-rium constant on temperature.The thermodynamics of Pb(II)adsorption onto the tobaccostems indicated that the adsorption was spontaneous and ngmuir and Fre-undlich isotherms were used to analyze the equilibrium data at different temperatures andthe equilibrium data were found tofit Freundlich isotherm equation better than Langmuirisotherm.The adsorption was analyzed using pseudo-second-order kinetic equation.©2008Elsevier B.V.All rights reserved.1.IntroductionMany industries such as electroplating,metal-processing,paint,plastics alloy,batteries,ammunition and the ceramicglass industries and so on generate large quantities of wastew-ater containing various types and concentration of heavymetals.Although many heavy metals are necessary in smallamounts for the normal development of the biological cycles,most of them become toxic at high concentrations.The heavymetal pollution is of greatest concern among the kinds ofenvironmental pollution because of heavy metals’high tox-icity and mobility.It is well documented that lead is oneof contaminants of industrial wastewaters and its pollutionexists in the wastewater of many industries(Sekar et al.,2004).Unlike most organic pollutants,heavy metals do not∗Corresponding author at:Faculty of Materials and Metallurgical Engineering,Kunming University of Science and Technology,Kunming 650093,PR China.Tel.:+868715192076;fax:+868715191046.E-mail address:jhpeng ok@(J.Peng).undergo biological degradation and tend to accumulate inthe organisms,thereby eventually entering the food chains(Qin et al.,2006).All the chemicals/compounds containinglead are considered as cumulative poisons(Nadeema et al.,2006).Lead poisoning in human causes severe damage tothe kidney,nervous system,reproductive system,liver andbrain.Severe exposure to lead has been associated with steril-ity,abortion,stillbirths and neonatal deaths(Bhattacharjeeet al.,2003;Goyer and Chisolon,1972;T unali et al.,2006).In industrial wastewaters,lead ion concentrations approach200–500mg L−1;this value is very high in relation to waterquality standards,and Pb(II)concentration of wastewatersshould be reduced to a value of0.1–0.05mg L−1.The permis-sible level for lead in drinking water is0.05mg L−1accordingto the World Health Organization(1984).Therefore,a very low0926-6690/$–see front matter©2008Elsevier B.V.All rights reserved.doi:10.1016/j.indcrop.2008.03.007i n d u s t r i a l c r o p s a n d p r o d u c t s28(2008)294–302295concentration of lead in water is very toxic.Hence,the safe and effective disposal of wastewater containing heavy metals is always a challenge to industrialists and environmentalists (Bhattacharjee et al.,2003).In wastewater treatment technology,various techniques have been used for lead ions removal.An effective method for lead ions removal is chemical precipitation with lime or alkali hydroxide.However,disposal of large quantities of sludge is difficult.The commonly used traditional methods for the removal of heavy metal ions from aqueous solu-tions include ion exchange,electro-flotation,reverse osmosis, membranefiltration,electrochemical treatment,and evapo-rative recovery.These conventional techniques are costly and have significant disadvantages such as generation of metal-bearing sludge or wastes,incomplete metal removal,the disposal of secondary waste.For these reasons,there is a need for developing economic and eco-friendly methods for waste minimization andfine-tuning of the wastewater(Ayyappan et al.,2005).Adsorption is an attractive process,in view of its effi-ciency and the ease with which it can apply to the treatment of wastewater containing heavy metals.Over last few decades adsorption has gained importance as an effective purifica-tion and separation technique used in wastewater treatment. The economics of this process depends mainly on the cost of the adsorbent materials.Although commercial activated carbon,with high surface area,microporous character and high adsorption capacity,has made its potential adsorbent for the removal of heavy metals from industrial wastewater,it is expensive,has relatively high operation costs.Thus,low cost adsorbents are becoming the focus of many investigations on the removal of heavy metals from aqueous solutions.In recent years,various adsorbents have been used for the removal of Pb(II)from aqueous solution(Ayyappan et al.,2005;Bereket et al.,1997;Bhattacharjee et al.,2003;Demirbas et al.,2005; Doyurum and Celik,2006;Feng et al.,2004;Li et al.,2007;Liu et al.,2006;Sari et al.,2007;Sekar et al.,2004;T unali et al.,2006). However,new adsorbents with locally available,high adsorp-tion capacity and economic materials are still needed.Low cost adsorbents could be produced from many raw materials such as agricultural byproducts and industrial wastes.Tobacco is a kind of important crop and has special eco-nomical value.According to statistical yearbook of China (2004),the output of tobacco leaf in the year2003was2.2 million tons in Yunnan province,which was65.5%of whole national output.Its output of tobacco stems reached about 1.5million tons which equals to that of tobacco leaf.Unfortu-nately,the agricultural and industrial activities derived from such crop generate waste that constitutes a serious environ-mental problem.At the present time,tobacco stems almost became waste after tobacco leaf reaped.Most of tobacco stems were discarded as solid waste or burned off in stacks or used as mulch.Generally speaking,it breaks the balance of ecological environment and produced the environmental contamination and air pollution.On the other hand,the useful and renewable resources are wasted.So,it is very significant to explore multi-purpose utilization technologies to dispose tobacco stems. In our group,we have prepared high surface area activated carbons(Li et al.,2008a)and woodceramics(Li et al.,2008b) successfully using tobacco stems as raw materials.To our knowledge,compared with other adsorbents no information exists on the use of tobacco stems,as an adsorbent for the removal of lead(II)ions and also needs to research.For this purpose,in the present study,adsorption of lead(II)ions onto tobacco stems,a typical agricultural byproduct,was investi-gated systematically with the variation in the parameters of pH,dosage,contact time,the initial concentration of adsor-bate,and ngmuir and Freundlich isotherms were used to analyze the equilibrium data at different tem-peratures.The kinetics of Pb(II)adsorption system has been studied based on the assumption of a pseudo-second-order law.2.Experimental and methods2.1.Materials and chemicalsAll chemicals used were of analytical reagent grade;anhy-drous lead nitrate(Acros,Corp.)was used without any further purification.Stock lead solution was prepared using anhydrous lead nitrate dissolved in distilled water.Working standards were prepared by progressive dilution of stock lead solution using deionized water.Tobacco stems,a typical agricultural waste,were collected from Yuxi city,Yunnan Province,P.R.China.The raw materi-als were washed thoroughly with deionized water,and dried at100◦C,crushed and sieved to particles with size range of 40–60mesh for use as adsorbent.2.2.InstrumentationThe concentration of lead ions was determined by AAS method.The difference in concentrations was taken as the amount of lead adsorbed by the tobacco stems.An atomic adsorption spectrometer(Solaar M6,USA),with lead hallow cathode lamp and air acetyleneflame,was used for determin-ing lead concentration.A digital pH meter(PHS-29A,Shanghai, China)was used for pH measurements.The pH meter was standardized using buffer solutions(sodium tetraborate and mixed phosphate)of pH values9.18and6.86.An electrically thermostatic reciprocating shaker(HQ45Z,Wuhan,China) was used for agitating the samples.2.3.Batch adsorption studiesBatch adsorption experiments were conducted at desired pH value,contact time and adsorbent dosage level using neces-sary adsorbents in a150mL capped conicalflask containing 50mL of test solution on an electrically thermostatic recipro-cating shaker.Weighed the different amount of adsorbents, tobacco stems(0.1,0.3,0.5,0.8,1.2,1.5and2.0g)into the con-icalflasks,and thoroughly mixed with Pb2+solutions(50mL) of the different initial concentrations(10,30,50mg L−1). Adjusted the pH of solution with HNO3(0.1,0.01mol/L)and NaOH(0.1,0.01mol/L)to the desired initial values(pH5.0), then put the conicalflasks onto the vibrator to shake120min to reach adsorption equilibrium at thefixed shaking speed (184rpm)and different temperatures(26,30,35,40◦C).After reaching equilibrium,the mixture wasfiltered through What-manfilter paper and determined the concentrations of lead296i n d u s t r i a l c r o p s a n d p r o d u c t s28(2008)294–302ions infiltrate by AAS.Control experiments were conducted under the same experimental conditions using deionized water without Pb2+.All of the batch experiments were car-ried out in duplicate and the values reported are average of two readings.Based upon initial andfinal concentrations of Pb(II)solution,we could calculate the adsorption constant of Pb(II)on tobacco stems.The residual metal concentration was obtained by calculating the difference between the initial and final metal concentration in solution.Percentage removal of Pb2+was calculated as removal(%)=(1−C t/C0)×100,and the amount of solute adsorbed per unit weight of the adsorbent at different times,or the adsorption capacity,was calculated by equation q t=(C0−C t)V/M,where q t(mg g−1)represented the adsorption capacity;C0and C t(mg L−1)were the aqueous phase solute concentrations(mg L−1)initially and at time t, respectively;V(L)was the volume of solution taken for the adsorption experiment;M(g)was the weight of adsorbent.2.4.Adsorption kineticsThe prediction of kinetics is necessary for the design of adsorption systems.The kinetic parameter,which is help-ful for the prediction of adsorption rate,gives important information for designing and modeling the processes.Thus, the effects of initial concentration,contact time,and adsor-bent dosage were analyzed from the kinetic point of view. Throughout the study,the effects of initial lead ion concen-trations(10–50mg L−1),contact time(5–240min),pH(2.0–6.0) and dosage of adsorbent(0.1–2.0g)on the removal of Pb(II) were investigated systematically.The apparatus used in the kinetics experiments were similar to those used in the batch experiments.3.Results and discussion3.1.Effects of contact time on adsorptionEffects of contact time on the removal of lead were illustrated in Fig.1.Experimental studies were carried out at temper-ature299K with varying initial metal ion concentrations of lead10,30,50mg L−1using dosage of0.8g adsorbent at pH 5.0.It was observed that the lead removal increased with con-tact time and was rapid for thefirst50min and thereafter it proceeded at a lower rate andfinally attained saturation.Equi-librium adsorption was established within120min for metal ions at initial concentration of10,30and50mg L−1.It was very clear from the results that the contact time required for maxi-mum uptake of metal ions by tobacco stems was dependent on the initial metal ion concentration.Lead removal was highly concentration dependent.In fact,the more concentrated the solution,the better the adsorption.This result is important because equilibrium time is one of the parameters for eco-nomical wastewater treatment plant application(Kadirvelu and Namasivayam,2003).Above behavior suggests that at the initial stage,adsorption takes place rapidly on the external surface of the adsorbent followed by a slower internal diffu-sion process,which may be the rate-determining step.The trend in adsorption of Pb(II)suggests that the binding may be through the interactions with functional groups located onthe Fig.1–Effects of contact time on lead ions removal at various concentrations(adsorbent dosage:0.8g;pH:5.0; temperature:299K).surface of the tobacco stems.According to these results,the contact time wasfixed at120min for the batch experiments to make sure that equilibrium was attained.The removal of lead ions for concentrations10,30and50mg L−1at contact time 120min were94.37%,92.10%and90.43%,respectively.The results demonstrated that at afixed adsorbent dosage, the amount adsorbed increased with increasing concentra-tion of solution,but the percentage of adsorption decreased. At lower concentrations,the ratio of number of metal ions to the available adsorption sites is low and subsequently the fractional adsorption becomes independent of initial concen-tration.At higher concentrations,however,the available sites of adsorption become fewer and subsequently the removal of metals depends on the initial concentrations.Hence,the removal of lead depends on the initial lead ion concentrations and decreases with increase in initial lead ion concentra-tion.3.2.Effects of dosage of adsorbent on adsorptionEffects of dosage on the removal of lead ions were presented in Fig.2.Experimental studies were carried out at tempera-ture299K with varying initial metal ion concentrations of lead 10,30,50mg L−1using contact time120min at pH5.0.It was shown that the removal of lead increased rapidly with increas-ing dosage from0to0.5g,after certain adsorbent dosage the removal efficiency was not increased significantly and reached the maximum at dosage of0.8g.The removal of lead for10, 30and50mg L−1using0.8g adsorbent was94.37%,92.10% and90.43%,respectively.The variation in adsorption capac-ities between the various adsorbent dosages could be related to the type of surface group responsible for the adsorption of metal ions from solution.With increasing adsorbent dosage more surface area is available for the adsorption due to an increase in active sites on the adsorbent and its availability for adsorption,making easier penetration of lead(II)ions to the adsorption sites and that increasing this number had no effect after equilibrium was reached.i n d u s t r i a l c r o p s a n d p r o d u c t s 28(2008)294–302297Fig.2–Effects of dosage on lead ions removal at various concentrations (contact time:120min;pH:5.0;temperature:299K).3.3.Effects of pH on adsorptionThe pH of the aqueous solution is an important control-ling parameter in the adsorption process.Earlier studies have shown that the most critical parameter in the treatment of heavy metal by adsorbents is the initial pH of the adsorp-tion medium.Since the pH of aqueous solutions influences the solution chemistry of the heavy metals (i.e.,hydrolysis,complexation,redox reactions,and precipitation),and the solution chemistry of the heavy metals also strongly influ-ences the speciation and the adsorption availability of the heavy metals,the binding of metal ions by surface functional groups is strongly pH-dependent (Lee and Davis,2001).This is partly because hydrogen ions themselves are strongly com-peting with metal ions.The effect of pH on the lead removal (absorbent dosage 0.80g,contact time 120min,temperature 299K)was shown in Fig.3.It was observed that the solution pH affected the amount of lead adsorbed.The lead uptakewasFig.3–Effects of pH on lead ions removal at various concentrations (absorbent dosage:0.80g;contact time:120min;temperature:299K).found to increase with increasing pH,and it increased rapidly for an increase in pH from 2to 3.For three solutions of different initial Pb(II)concentrations (10,30,50mg L −1),the maximum removal of lead appeared at pH 5.0.The increase in metal removal as pH increases could be explained on the basis of a decrease in competition between hydronium ions and metal species for the surface sites and also by the decrease in posi-tive surface charge on the adsorbent,which resulted in a lower electrostatic repulsion between the surface and the metal ions and hence uptake of metal ions increased.A similar theory was proposed by several earlier workers for metal adsorp-tion on different adsorbent (Acar and Eren,2006;Bhattacharya et al.,2006;Srivastava et al.,2006).In alkaline medium,lead tends to hydrolyze and precipitate instead of adsorption and adsorbent was deteriorated with accumulation of metal ions,making true adsorption studies impossible (T unali et al.,2006;Sari et al.,2007;Bereket et al.,1997;Doyurum and Celik,2006;Liu et al.,2006).Therefore,pH 5was selected to be the opti-mum pH for all further studies.3.4.Effects of temperature on adsorptionThe temperature is an important parameter in the context of adsorption on solid phase and has two major effects on the adsorption process.Increasing the temperature is known to increase the rate of diffusion of the adsorbate molecules across the external boundary layer and in the internal pores of the adsorbent particle,owing to decrease in the viscos-ity of the solution.In addition,changing temperature will change the equilibrium capacity of the adsorbent for a par-ticular adsorbate (Al-Qodah,2000;Dogan et al.,2004).In the present case,effects of temperature on the extent of solute adsorption were investigated systematically at different tem-peratures (26,30,35,40◦C)under the selected agitation time (120min)and dose of adsorbents (0.8g).Adsorption reactions are normally exothermic (Sarkar and Acharya,2006a ).As the temperature increases the percentage adsorption decreases in accordance with Le Chatelier’s principle.The decrease in percentage uptake may be due to a decreased equilibrium constant for adsorption at higher temperature.The equilib-rium extent or capacity of adsorption in a given system is thus found to decrease with the increase of temperature.In the present case,the removal rate increased as temper-ature increased,indicating that the adsorption of lead onto tobacco stems was an endothermic process ( H ◦was positive value).3.4.1.Thermodynamics parametersA study of the temperature dependence of adsorption reac-tions gives valuable knowledge about the enthalpy and entropy changes during adsorption.The standard Gibbs free energy change ( G ◦)is the fundamental criterion of spon-taneity of a process and can be determined using equilibrium constant (K c )by equation: G ◦=−RT ln K c(1)where R is the universal gas constant (1.987cal K −1mol −1,or 8.314J mol −1K −1)and T is the temperature in Kelvin (K).The equilibrium constant,K c ,the Langmuir adsorption constant,298i n d u s t r i a l c r o p s a n d p r o d u c t s 28(2008)294–302Fig.4–Van’t Hoff plot for Pb ions adsorption onto tobacco stems.can be calculated as K c =C aeC e,(2)where C ae and C e represent the equilibrium solute concen-tration on the adsorbent and in the solution,respectively.The standard enthalpy change ( H ◦)and standard entropy change ( S ◦)were given by Van’t Hoff equation that showed the dependence of equilibrium constant of the adsorption pro-cess on the temperature. G ◦= H ◦−T S ◦,(3)ln K c =S ◦R − H ◦RT.(4)The plot of ln K c against 1/T was found to be linear;hencethe H ◦and S ◦could be calculated from the intercept and slope of the plot ln K c versus 1/T ,shown in Fig.4(adsorbent dosage 0.8g,contact time 120min,pH 5.0,initial concentra-tion 30mg L −1,temperature 299K)and the thermodynamic parameters ( G ◦, H ◦, S ◦)at four temperatures (299,303,308,313K)were listed in Table 1.The standard Gibbs free energy change G ◦at all temperatures was negative value,confirming that the adsorption of lead onto tobacco stems was spontaneous and thermodynamically favorable.The more negative the G ◦,the stronger the driving force of adsorption reaction.The standard enthalpy change H ◦(1.124kJ mol −1)was positive value,so the adsorption of lead onto tobacco stems was an endothermic process.The positive adsorption1–Thermodynamic parameters for Pb(II)onto tobacco stems at various temperatures T (K)G ◦(kJ mol −1) H ◦(kJ mol −1) S ◦(J mol −1K −1)294−6.1054 1.124024.1855303−6.2079308−6.3245313−6.4454standard entropy change S ◦(24.1855J mol −1K −1)may be interrelated to the increased randomness at the solid–liquid interface.3.5.Adsorption isothermsAdsorption isotherm is a functional expression that corre-lates the amount of solute adsorbed per unit weight of the adsorbent and the concentration of an adsorbate in bulk solu-tion at a given temperature under equilibrium conditions.It is important to establish the most appropriate correlations for the batch equilibrium data using empirical or theoretical equations as it plays a functional role in predictive model-ing procedures for analysis and design of adsorption systems.The adsorption isotherms are one of the most useful data to understand the mechanism of the adsorption and the char-acteristics of isotherms are needed before the interpretation of the kinetics of the adsorption process.Many models have been proposed to explain adsorption equilibrium,however,no general model has been found to fit the experimental data accurately under any given condition.A particular one that fits the data under one set of conditions may completely mis-fit under another.The most widely used isotherm models for solid–liquid adsorption are the Langmuir and Freundlich isotherms.They can be used to describe the equilibrium adsorbed metal ions and metal ions in solution.In the present investigation,the experimental data were tested with respect to both these isotherms.The Langmuir model was originally developed to represent chemisorption on a set of well-defined localized adsorption sites having the same adsorption energy,independent of the surface coverage and with no interaction between adsorbed molecules (Langmuir,1918).The Langmuir isotherm further based on the assumption that all the adsorption sites are energetically identical (monolayer adsorption)and adsorp-tion occurs on a structurally homogeneous adsorbent.So this model is also called the ideal localized monolayer model.For solid–liquid systems,the Langmuir isotherm is given as:q e =K L C e1+a L C e.(5)The linear form of the Langmuir isotherm is given by equa-tionC e q e =1K L +a L C eK L(6)where K L (dm 3g −1)and a L (dm 3mg −1)represent Langmuir constants;the K L /a L values provide a measure of the maxi-mum adsorption capacity q max (mg g −1)in the system;q e is the amount of solute adsorbed per unit weight of adsorbent (mg g −1)at equilibrium,C e is the equilibrium solute concen-tration in solution (mg dm −3).The essential characteristics of the Langmuir isotherm can also be expressed in terms of a dimensionless constant sepa-ration factor or equilibrium parameter,R L ,which is defined as (Weber and Chakravorti,1974).R L =1(1+a L C 0),(7)i n d u s t r i a l c r o p s a n d p r o d u c t s28(2008)294–302299where a L(dm3mg−1)is the Langmuir constant and C0(mg dm−3)is the initial concentration of adsorbate.The R Lvalue indicates the shape of the isotherm as follows.R L value T ype of isothermR L>1UnfavorableR L=1Linear0<R L<1FavorableR L=0IrreversibleAccording to Mckay et al.(1982),R L values between0and1indicate favorable adsorption.In the present study,for initialconcentration of Pb(II)30mg L−1,the R L was0.136,0.157,0.172and0.171at different temperatures,respectively,indicatingthat the adsorption of lead ions onto the tobacco stems wasfavorable.The results were in agreement with the results ofthermodynamics data,which had shown the adsorption wasendothermic and spontaneous.The Freundlich adsorption isotherm usuallyfits the exper-imental data over a wide range of concentrations(Freundlich,1906).Freundlich isotherm gives the relationship betweenequilibrium liquid and solid phase capacity based on the mul-tilayer adsorption(heterogeneous surface).This isotherm isderived from the assumption that the adsorption sites are dis-tributed exponentially with respect to the heat of adsorptionand is given by:q e=a f C b f e(8)and linearized as:ln q e=ln a f+b f ln C e(9)where a f(mg g−1)indicates the multilayer adsorption capac-ity and b f an empirical parameter related to the intensity ofadsorption,which varies with the heterogeneity of the adsor-bent.For values in the range0.1<b f<1,adsorption is favorable.The greater the values of b f better is the favorability of adsorp-tion.The adsorption studies were conducted at afixed adsorbentdosage by changing initial lead ion concentration.The equi-librium data were analyzed using Langmuir and Freundlichequilibrium models(Eqs.(6)and(9))in order to obtain thebest-fit isotherm.ngmuir isothermThe plot of C e/q e versus C e was shown in Fig.5.The slope andintercept represented the a L/K L and1/K L,respectively,so theK L and a L could be calculated from the slope and interceptof plot.The Langmuir equilibrium adsorption curves relatingsolid and liquid phase concentrations for lead onto the tobaccostems at different temperatures are given as follows:299K q e=1.1747C e(1+0.2119C e)(10)303K q e=1.1810C e(1+0.2120C e)(11)Fig.5–Langmuir isotherm profiles for the adsorption oflead(II)ions onto tobacco stems at various temperatures.308K q e=1.1215C e(1+0.1943C e)(12)313K q e=1.1270C e(1+0.1946C e).(13)3.5.2.Freundlich isothermThe plot of ln q e versus ln C e was illustrated in Fig.6.The slopeand intercept represented the b f and ln a f,,respectively,so theb f and a f could be calculated from the slope and interceptof plot.The equilibrium curves given by Freundlich isothermwere given as follows:299K q e=0.9474C0.7233e(14)303K q e=0.9474C0.7233e(15)308K q e=0.9606C0.7285e(16)313K q e=0.9522C0.7234e.(17)3.5.3.Evaluation of isotherm modelsThe adsorption capacity predicted by the two isotherms werecompared and the corresponding Langmuir and Freundlichisotherm parameters,along with the regressioncoefficientsFig.6–Freundlich isotherm profiles for the adsorption oflead(II)ions onto tobacco stems at various temperatures.300i n d u s t r i a l c r o p s a n d p r o d u c t s28(2008)294–3022T(K)Langmuir constants Freundlich constantsq max(mg g−1)a L(L/mg)R a f(mg g−1)b f R299 5.54350.21190.98300.94740.72330.9951 303 5.57100.21200.98890.94740.72330.9999 308 5.77070.19430.98370.96060.72850.9995 313 5.79210.19460.98360.95220.72340.9971(q max,a L,a f,b f and R)at different temperatures were summa-rized in Table2.The values of q max indicate good adsorption efficiency.This demonstrates that the tobacco stems adsor-bent has good adsorption efficiency for Pb removal.It is observed from isotherms and regression coefficients that the fit is better with the Freundlich model than with the Lang-muir model.The Langmuir and the Freundlich models could be used to describe the adsorption data well,showing the fact that both monolayer and heterogeneous surface conditions exist under the experimental condition used,implying that the adsorption of Pb2+ions onto the tobacco stems is thus complex and involve more than one mechanism.The validity of the Langmuir model suggests the adsorp-tion process is monolayer and adsorption of each molecule has equal activation energy.The magnitude of Langmuir con-stant a L is largely determined by the heat of adsorption.The a L values change from0.2119to0.1946L/mg.Further,the energy of the process at all temperatures was negative and increased with increasing the temperature,which indicated that the pro-cess was spontaneous in nature and the spontaneity increased with the rise of temperature.This further supported the mech-anism above.Thus,the Langmuir model reduces to Henry’s law at low concentration;i.e.,as C e becomes lower,the a L C e (Eq.(5))tends to a value less than unity and follows Henry’s law,whereas the Freundlich model does not reduce to the lin-ear isotherm at low surface coverage.Freundlich values of b f between0.7233and0.7234(0.1<b f<1)showed the favorabil-ity of adsorption of Pb(II)onto tobacco stems.The regression coefficients of both models showed a strong affinity for the adsorption of Pb(II)on the tobacco stems.3.6.Adsorption kineticsThe kinetics of adsorption describes the rate of metal ions uptake on tobacco stems and this rate controls the equilibrium time.The kinetics of adsorbate uptake is required for selecting optimum operating conditions for the full-scale batch process, so these models are important in water treatment process design.The kinetic parameter,which is helpful for the pre-diction of adsorption rate,gives important information for designing and modeling the process.Thus,the effects of ini-tial concentration,contact time,and adsorbent dosage were analyzed from the kinetic point of view.Adsorption kinetics are generally controlled by different mechanisms,of which the most limiting are the diffusion mechanisms,including the initial curved portion,attributed to rapid external diffusion or boundary layer diffusion and sur-face adsorption,and the linear portion,a gradual adsorption stage due to the intraparticle diffusion,followed by a plateau to the equilibrium where the intraparticle diffusion starts to decrease due to the low concentration in solution phase as well as fewer available adsorption sites(Guibal et al.,2003). Previously several researchers used different kinetic models, such as Lagergren’s pseudo-first-order,pseudo-second-order, Elovich kinetic equation,and parabolic diffusion model,to represent the mechanism of the adsorption process(Hoda et al.,2006;Sarkar et al.,2006b;Weber and Morris,1963). Currently the pseudo-second-order model has been widely used for adsorption systems due to its good representation of the experimental data for most of the adsorbent–adsorbate systems(Ho and McKay,1999).The pseudo-second-order equation has following advantages:it does not have the problem of assigning an effective adsorption capacity,the adsorption capacity,rate constant of pseudo-second-order and the initial adsorption rate all can be determined from the equation without knowing any parameter beforehand.So,in the present study,the applicability of pseudo-second-order model has been tested for the adsorption of lead onto the tobacco stems.Adsorption kinetics was explained by the pseudo-second-ordermodel given by Ho and McKay(1998a)as follows:d qd t=k2(q e−q)2.(18)Integrating Eq.(3)for the boundary conditions q=0to q=qt at t=0to t=t is simplified astq t=1k2q2e+1q et(19) h=k2q2e(20)Fig.7–Pseudo-second-order kinetics plots for the adsorption of lead(II)ions onto tobacco stems.。
