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1、 改性的植物废物吸附废水中重金属离子目前处理废水的方法大致分为物理法、化学法（化学沉淀、离子交换、电浮法、膜分离、反渗透、电渗、溶液萃取等）和生物吸附法(微生物吸附和植物吸附），然而物理法和化学法操作难度大，费用高，容易产生二次污染，生物吸附法中植物吸附成本低，操作简单，来源广泛，所以植物废物吸附重废水中金属离子成为了科学研究的重点。 1重金属废植物废物吸附剂的改性研究简述 1.1未处理的植物废物吸附剂的优缺点植物废物吸附剂大多由纤维素组成，来源丰富，包含木瓜木、玉米叶、茶叶粉、白茅叶粉、香蕉叶粉、花壳颗粒、西米、椰子树、蕨类植物、稻壳灰和印树皮等等。植物废物处理废水的优点包括技术简单，吸附时
2、中几乎不需要复杂过程，有良好的吸附能力，选择性吸附重离子，低消耗，免费可用，容易再生，然而，未处理的植物废物吸附剂的应用也带来了一些问题，比如，低吸附效能、耗氧量（COD)、生物化学需求(BOD)以及由于植物废物中可溶性有机物释放的有机碳(TOD)的增长能引起水中氧气大量消耗，这威胁到水生生物的生命，因此在用于净化重金属之前，植物废物需要处理。 1.2改性后的植物废物吸附剂 改性后的植物废物表现出对重金属离子良好的吸附性能，稻米壳、甘蔗蔗渣、粉煤灰、锯屑、麦糠等经处理后，对某些重金属离子的吸附量、吸附速率显著提高，但用不同改性试剂处理后吸附效果不同,所以要选择合适的改性试剂。 1.3改性的植物
3、废物吸附剂的分类根据吸附剂分子中引入的吸附基团的种类和吸附方式的不同，可以将吸附剂分为阳离子吸附剂，阴离子吸附剂，两性吸附剂，离子螯合吸附剂。 1.4改性后的植物废物吸附剂的制备 首先用清水初洗抽滤烘干，筛筛选合适粒径颗粒，其次使用合适的有机试剂除去植物色素、一些极性物质，并去离子水洗涤二次洗涤，抽滤烘干，最后用矿物质，有机酸，碱溶液，氧化剂，有机化合物等改性化学试剂处理，待备用。 2吸附机理的分析重金属离子扩散到表面并沉积；重金属离子扩散到吸附中心发生离子交换；重金属离子与含氧官能团发生化学吸附，如发生络合反应、氧化还原反应等，溶质从水中移向固体颗粒表面发生吸附的过程是水、溶质和吸附剂间作用
4、的结果，发生吸附的主要原因在于溶质对水的疏水性和溶质对颗粒的较高亲和力。植物废物经改性后，引入了大量的表面活性基，增强了吸附剂吸附能力。 3吸附效率的影响因素3.1PH值的影响 当废水pH值较低时，一方面H+将与目标离子竞争活性吸附位点，高度质子化，目标离子参与的活性吸附位点减少，从而对金属离子的吸附量减少，PH值过高时，金属离子将与-OH生成沉淀，处于负离子氛围中，不利于和吸附剂发生反应，因而需选择最佳PH值吸附范围。3.2温度的影响 一般情况下，温度对吸附的影响不大，若吸附是放热过程，则吸附剂吸附能力随温度的升高而降低；若吸附是吸热过程，则吸附剂吸附能力随温度的升高而升高；此外温温度较高时
5、随着溶液温度的增加其粘度降低，从而增加了溶质分子的分散速率。吸附剂不同，吸附作用机制也各异，温度对重金属离子吸附量的影响也有差异。 3.3接触时间的影响 随时间的增加植物废物吸附量逐渐增加，但当到达一定时间，吸附达到平衡，此时 植物废物内部孔隙都已经达到饱和，吸附质很难被吸附在吸附剂表面。 3.4重金属初始浓度和吸附剂的浓度吸附效率跟重金属初始浓度与植物废物浓度比有关，两者比值越大，植物废物吸附量越大，除非达到饱和状态。比值越大，重金属对植物废物表面积和活性位点的利用越充分，吸附效率高。 3.5其他杂质离子的影响 在混合溶液中需要考虑其他离子对目标离子吸附的影响，目标离子同其他离子可能存在协同
6、，拮抗和加和作用，关键是否与目标离子争夺吸附位点，还是发生亲和作用。 3.6吸附剂粒径孔隙的影响 颗粒的比表面积和孔容越大吸附剂的吸附能力越强，应筛选指定孔容和表面积的颗粒，一般以粒径为依据筛选，此外孔隙扩散速率是制约吸附的主要速率的主要原因，经改性的吸附剂颗粒比表面积和孔隙结构发生变化，进而影响吸附剂吸附效率。 4改性的花生壳对铬吸附情况的简述铬离子废液PH为1-2，接触时间为100min、花生壳浓度与铬离子初始浓度比为200/1，粒径为0.25-0.5mm时吸附效率最高。 5植物废物吸附剂的应用改性植物废物可广泛应用于吸附废水中重金属离子，医药，半导体应用等，解决海洋污染和生活用水污染问题
7、。最佳吸附剂材料和改性物质的选择成为研究者们研究的重点。 6植物废物吸附剂的发展前景 农林废弃物是一种来源丰富的可再生资源，将植物废物用于工业废水，不仅可以降低废水污染，而且降低废水处理成本，为植物废物综合利用提供新途径，农林废弃物的合理开发利用必将带来巨大的经济利益和社会效益，然而植物废物吸附剂对重金属吸附具有高度选择性，所以仍需克服这一限制。河北师范大学汇华学院本科生毕业论文（设计）翻译文章摘要：纤维质的植物废料可作为廉价的吸附剂除去重金属离子，它们除去重金属离子的性能受化学处理的影响，通常，化学改良的植物废料与未改良的相比，能显示出更强的吸附能力，这些化学修饰物包括矿物质、有机酸、碱溶液
8、、氧化剂、有机化合物等等，这次研究了包含大米壳花粒、锯末、甘蔗蔗渣、水果废弃物、杂草等的植物废料吸附剂。关键词：吸附 植物废物 廉价吸附剂 重金属 废水处理1介绍 由于高速发展的工业化，重金属过量地释放到环境中，在工业废水中常检测到镉、锌、铜、镍、铅、汞和铬。这源于金属电镀、采矿活动、冶炼、电池制造、印刷摄影等工业。不像有机废物，重金属不可降解，它们在活组织中积累，导致各种疾病和失调症，因此必须在它们释放前除去。研究者用廉价的吸附剂产品取代昂贵的，废水处理的方法如化学沉淀、离子交换、电浮法、膜分离、反渗透、电渗、溶液萃取等正在吸引科学家的关注，吸附作用是一种物化处理方法，能有效地除去水中的重金
9、属，许多吸附作用的研究已经聚焦在未处理的植物废物上，例如木瓜木、玉米叶、茶叶粉、白茅叶粉、香蕉叶粉、花壳颗粒、西米、椰子树、蕨类植物、稻壳灰和印树皮等等。植物废物处理废水的优点包括技术简单，几乎不需要复杂过程，有良好的吸附能力，选择性吸附重离子，低消耗，免费可用，容易再生，然而，未处理的植物废物吸附剂的应用也带来了一些问题，比如，低吸附效能，耗氧量（COD)、生物化学需求(BOD)以及由于植物废物中可溶性有机物释放的有机碳(TOD)的增长能引起水中氧气大量消耗，这威胁到水生生物的生命，因此在用于净化重金属之前，植物废物需要处理。 2.化学改良的植物废物 植物废物的预处理能提取出可溶性有机物，增
10、强螯合效能，使用改良剂的不同处理方法不同，如碱性溶液（氢氧化钙、碳酸钠），矿物质和有机酸溶液（盐酸、硝酸、硫酸、酒石酸、柠檬酸、氢硫基乙酸），有机化合物（乙二胺、甲醛、氯乙醇、甲酸），氧化剂（过氧化氢）及染料（活性橙13）等，为除可溶性有机化合物，除去水溶液的颜色，增加重金属吸附效率，许多科学家己经研究，各种用于改良废物的化学药品和他们的最大吸附能力已经展示在表格1中。2.1稻米壳稻壳是由纤维素32.24%，半纤维素21.34%，木质素21.44%和矿物质火山灰15.05%以及大量硅灰矿物质（比例高达96.34%）组成，稻壳不溶于水，良好的化学稳定性，具有较高的机械强度和粒状结构，这使它成为除
11、去废水中重金属良好的吸附材料，盐酸氢氧化钠、碳酸钠、环氧氯丙烷和酒石酸通常用于化学处理稻米壳，预处理的稻壳能移除木质素、半纤维素，降低纤维素结晶度，增加孔隙度或表面积,一般地，化学改良过的稻米壳比未改良的稻米壳显示出更高的吸附能力。同时，用于处理植物废物的大多数酸都是稀酸，如盐酸、硫酸和硝酸。据Esteghlalian莲等。（1997）使用稀硫酸预处理能提高反应速率和加快纤维素的水解，浓缩酸是水解纤维素的有力试剂，但是他们是有毒的，腐蚀性的，必须被还原，然而在某些情况下，盐酸处理的稻壳对镉吸附能力不如未处理的稻米壳，（Kumar和Bandyopadhyay，2006）。这由于米壳表面的吸附部位
12、将会被质子化，重金属无法被吸附在吸附剂表面。Wong等(2003a)对各种被羧酸（柠檬酸、水杨酸、酒石酸、草酸、扁桃酸、苹果酸和次氮基三乙酸）改性的米壳进行了铜和铅的吸附研究，酒石酸改良的米壳的吸附能力最高，然而酯化酒石酸改良米壳大大降低了对铜和铅的吸收，高摩尔比的螯合剂如次氮基三乙酸和次乙亚基四乙酸（EDTA）对铅的吸收具有抑制作用，为除去Cr（VI）、Ni（II）、Cu（II）、Zn（II）、Cd（II）、Hg（II）和Pb（II）. 改良植物废物作为除去水溶液中重金属离子的吸附剂的总结suemitsu等使用红色和黄色的普施安处理稻壳（1986）。大于80%的Cd(II)、 Pb(II)
13、和Hg(II)离子能够被这两种处理类型的吸附剂除去，而Cr(VI)为最低的移除比例(40%)。2.2谷物渣 Low等证明（2000）用氢氧化钠处理的谷物渣能增强对Pb(II)和Cd(II)离子的吸附性，然而盐酸处理过的谷物渣比未处理的吸附性要低，经基本处理后吸附性的增加可以解释为，因邻甲基酯组的水解，半乳糖醛酸的含量增加所导致。对于重金属吸附来说，最佳值范围是4-6。动力学研究表明，重金属吸附平衡吸附时间是120分钟遵循伪二阶模型，EDTA、次氮基三乙酸在摩尔比为1：1（金属:配体）能螯合重金属离子，大大降低了吸附能力，因此更多的重金属离子保留在溶液中而不是被吸附(Jeon and Park,
14、 2005)。另一方面水杨酸稍减少了对镉的吸附但是并没有影响铅的吸附。2.3甘蔗蔗渣/粉煤灰 Junior等(2006)用琥珀无水石膏改良甘蔗蔗渣处理水溶液中铜，镉和铅，甘蔗蔗渣是由纤维素(50%),多糖(27%)和木质素(23%)组成.这三种生物高分子的存在导致甘蔗蔗渣中富含羟基和酚基，化学修改这些基团后产生吸附剂材料新性能，在甘蔗蔗渣中的羟基使用琥珀酐能被转换成羧基，并和三种不同的化学物质（主要是NaHCO3,乙二胺，三亚乙基四胺）反应产生一些新性能的吸附材料，这些吸附材料对不同的重金属显示出不同的吸附能力，据发现用乙二胺，三亚乙基四胺处理的甘蔗蔗渣跟未处理的样品相比含氮量显著增加。动力学
15、研究表明，乙二胺和三亚乙基四胺改良的甘蔗蔗渣吸附Cu,Cd和Pb的平衡时间比用NaHCO3改良的吸附剂慢。可能由于在三亚乙基四胺改良甘蔗蔗渣中存在大量亲核点，三亚基四胺改良的蔗渣是除去镉和铅的最好吸附剂材料，当甘蔗蔗渣被甲醇改性时，得到的吸附剂并没显示出对镉的良好吸附能力(Ibrahim 等,2006). 过氧化氢是一种良好的氧化剂，用来除去吸附剂上附着的有机物质，过氧化氢处理的甘蔗蔗渣飞尘除去铬的时间（60min）比铅（80min）短,等温线研究显示铬最大的吸附能力比铅的高，然而两种金属的最大吸附记录值较低（铅和铬分别是2.5，4.35mg g-1），处理蔗渣飞尘的吸附机理没有讨论，但吸附膜
16、扩散控制在低浓度金属，颗粒扩散控制在更高金属离子浓度 3 结论 该审查显示，化学改性植物废料可以除去重金属，这个研究吸引了更多科学家的关注。广泛的低成本从化学改性植物废料中获得的吸附剂已经被研究和多数研究都集中在去除重金属离子，如镉，铜，铅，锌，镍和Cr（VI ）离子。最常见用于化学处理植物废物的是酸和碱。化学改性植物废料从溶液中吸附重金属的能力差别很大，化学改性在一般提高吸附剂的吸附能力。这可能是由于在改良后较多活性结合位点，更好的离子交换性能，以及新的官能团的形成有利于重金属的吸附。虽然化学改性植物废料可以增强重金属离子的吸附，使用的化学制品的成本和维护的方法也必须考虑以生产“低价”的吸附
17、剂。由于吸附剂表面可能会改变吸附剂的性质，建议对于化学改性植物废料的任何工作，表征研究涉及表面积，孔径大小，孔隙率研究，pHZPC等都要进行。 blOKSOUPCfIfCtinOLOOT ScienceDirect Review Bioresource Technology 99 (2008) 3935-3948 Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: A review W.S. Wan Ngah , M.A.K.M. HanafiahSchoo
18、l of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, MalaysiaReceived 3 April 2007; received in revised form 18 June 2007; accepted 18 June 2007 Available online 27 July 2007AbstractThe application of low-cost adsorbents obtained from plant wastes as a replacement for costly conventional
19、 methods of removing heavy metal ions from wastewater has been reviewed. It is well known that cellulosic waste materials can be obtained and employed as cheap adsorbents and their performance to remove heavy metal ions can be affected upon chemical treatment. In general, chemically modified plant w
20、astes exhibit higher adsorption capacities than unmodified forms. Numerous chemicals have been used for modifications which include mineral and organic acids, bases, oxidizing agent, organic compounds, etc. In this review, an extensive list of plant wastes as adsorbents including rice husks, spent g
21、rain, sawdust, sugarcane bagasse, fruit wastes, weeds and others has been compiled. Some of the treated adsorbents show good adsorption capacities for Cd, Cu, Pb, Zn and Ni. 2007 Elsevier Ltd. All rights reserved.Keywords: Adsorption; Plant wastes; Low-cost adsorbents; Heavy metals; Wastewater treat
22、ment1. IntroductionHeavy metals have been excessively released into the environment due to rapid industrialization and have cre-ated a major global concern. Cadmium, zinc, copper, nickel, lead, mercury and chromium are often detected in industrial wastewaters, which originate from metal plating, min
23、ing activities, smelting, battery manufacture, tanneries, petroleum refining, paint manufacture, pesticides, pigment manufacture, printing and photographic industries, etc., (Kadirvelu et al., 2001a; Williams et al., 1998). Unlike organic wastes, heavy metals are non-biodegradable and they can be ac
24、cumulated in living tissues, causing various diseases and disorders; therefore they must be removed before discharge. Research interest into the production of cheaper adsorbents to replace costly wastewater treatment methods such as chemical precipitation, ion-exchange, elec-troflotation, membrane s
25、eparation, reverse osmosis, elec-trodialysis, solvent extraction, etc. (Namasivayam and Ranganathan, 1995) are attracting attention of scientists. Adsorption is one the physico-chemical treatment pro-cesses found to be effective in removing heavy metals from aqueous solutions. According to Bailey et
26、 al. (1999), an adsorbent can be considered as cheap or low-cost if it is abundant in nature, requires little processing and is a by-product of waste material from waste industry. Plant wastes are inexpensive as they have no or very low eco-nomic value. Most of the adsorption studies have been focus
27、ed on untreated plant wastes such as papaya wood (Saeed et al., 2005), maize leaf (Babarinde et al., 2006), teak leaf powder (King et al., 2006), lalang (Imperata cylindrica) leaf powder (Hanafiah et al., 2007), rubber (Hevea brasili- ensis) leaf powder (Hanafiah et al., 2006b,c), Coriandrum sativum
28、 (Karunasagar et al., 2005), peanut hull pellets (Johnson et al., 2002), sago waste (Quek et al., 1998), salt-bush (Atriplex canescens) leaves (Sawalha et al., 2007a,b), tree fern (Ho and Wang, 2004; Ho et al., 2004; Ho, 2003), rice husk ash and neem bark (Bhattacharya et al., 2006), grape stalk was
29、tes (Villaescusa et al., 2004), etc. Some of the advantages of using plant wastes for wastewa-ter treatment include simple technique, requires little pro-cessing, good adsorption capacity, selective adsorption of heavy metal ions, low cost, free availability and easy regeneration. However, the appli
30、cation of untreated plant wastes as adsorbents can also bring several problems such as low adsorption capacity, high chemical oxygen demand (COD) and biological chemical demand (BOD) as well as total organic carbon (TOC) due to release of soluble organic compounds contained in the plant materials (G
31、aballah et al., 1997; Nakajima and Sakaguchi, 1990). The increase of the COD, BOD and TOC can cause depletion of oxygen content in water and can threaten the aquatic life. Therefore, plant wastes need to be modified or treated before being applied for the decontamination of heavy metals. In this rev
32、iew, an extensive list of adsorbents obtained from plant wastes has been compiled and their methods of modification were discussed. A comparison of adsorption efficiency between chemically modified and unmodified adsorbents was also reported.1. Chemically modified plant wastesPretreatment of plant w
33、astes can extract soluble organic compounds and enhance chelating efficiency (Gaballah et al., 1997). Pretreatment methods using different kinds of modifying agents such as base solutions (sodium hydroxide, calcium hydroxide, sodium carbonate) mineral and organic acid solutions (hydrochloric acid, n
34、itric acid, sulfuric acid, tartaric acid, citric acid, thioglycollic acid), organic compounds (ethylenediamine, formaldehyde, epi- chlorohydrin, methanol), oxidizing agent (hydrogen peroxide), dye (Reactive Orange 13), etc. for the purpose of removing soluble organic compounds, eliminating colourati
35、on of the aqueous solutions and increasing efficiency of metal adsorption have been performed by many researchers (Hanafiah et al., 2006a; Reddy et al., 1997; Taty-Cos- todes et al., 2003; Gupta et al., 2003; Namasivayam and Kadirvelu, 1997; S(5iban et al., 2006a; Min et al., 2004; Kumar and Bandyop
36、adhyay, 2006; Baral et al., 2006; Acar and Eren, 2006; Rehman et al., 2006; Abia et al., 2006; Shukla and Pai, 2005a, Low et al., 1995; Azab and Peterson, 1989; Lazlo, 1987; Wankasi et al., 2006). The types of chemicals used for modifying plant wastes and their maximum adsorption capacities are show
37、n in Table 1.1.1. Rice husks/rice hullsRice husk consists of cellulose (32.24%), hemicellulose (21.34%), lignin (21.44%) and mineral ash (15.05%) (Rahman et al., 1997) as well as high percentage of silica in its mineral ash, which is approximately 96.34% (Rahman and Ismail, 1993). Rice husk is insol
38、uble in water, has good chemical stability, has high mechanical strength and possesses a granular structure, making it a good adsorbent material for treating heavy metals from wastewater. The removal of heavy metals by rice husk has been extensively reviewed by Chuah et al. (2005). Among the heavy m
39、etal ions studied include Cd, Pb, Zn, Cu, Co, Ni and Au.Rice husk can be used to treat heavy metals in the form of either untreated or modified using different modification methods.Hydrochloric acid (Kumar and Bandyopadhyay, sodium hydroxide (Guo et al., 2003; Kumar and Bandyopadhyay, 2006), sodium
40、carbonate (Kumar and Bandyopadhyay, 2006), epichlorohydrin (Kumar and Bandyopadhyay, 2006), and tartaric acid (Wong et al., 2003a; Wong et al., 2003b) are commonly used in the chemical treatment of rice husk. Pretreatment of rice husks can remove lignin, hemicellulose, reduce cellulose crystallinity
41、 and increase the porosity or surface area. In general, chemically modified or treated rice husk exhibited higher adsorption capacities on heavy metal ions than unmodified rice husk. For example, Kumar and Bandyopadhyay (2006) reported that rice husk treated with sodium hydroxide, sodium carbonate a
42、nd epichlorohydrin enhanced the adsorption capacity of cadmium. The base treatment using NaOH for instance appeared to remove base soluble materials on the rice husk surface that might interfere with its adsorption property. Tarley et al. (2004) found that adsorption of Cd increase by almost double
43、when rice husk was treated with NaOH. The reported adsorption capacities of Cd were 7 and 4mgg1 for NaOH treated and unmodified rice husk, respectively.Meanwhile, most of the acids used for treatment of plant wastes were in dilute form such as sulfuric acid, hydrochloric acid and nitric acid. Accord
44、ing to Esteghla- lian et al. (1997), dilute acid pretreatment using sulfuric acid can achieve high reaction rates and improve cellulose hydrolysis. Concentrated acids are powerful agents for cellulose hydrolysis but they are toxic, corrosive and must be recovered (Sivers and Zacchi, 1995). However,
45、in some cases, hydrochloric acid treated rice husk showed lower adsorption capacity of cadmium than the untreated rice husk (Kumar and Bandyopadhyay, 2006). When rice husk is treated with hydrochloric acid, adsorption sites on the surface of rice husk will be protonated, leaving the heavy metal ions
46、 in the aqueous phase rather than being adsorbed on the adsorbent surface. Wong et al. (2003a) carried out an adsorption study of copper and lead on modified rice husk by various kinds of carboxylic acids (citric acid, salicylic acid, tartaric acid, oxalic acid, mandelic acid, malic and nitrilotriac
47、etic acid) and it was reported that the highest adsorption capacity was achieved by tartaric acid modified rice husk. Esterified tartaric acid modified rice husk however significantly reduced the uptake of Cu and Pb. The maximum adsorption capacities for Pb and Cu were reported as 108 and 29 mg g1,
48、respectively. Effect of chelators on the uptake of Pb by tartaric acid modified rice husk was also studied. It was reported that higher molar ratios of chelators such as nitrilotriacetic acid (NTA) and ethylenediamine tetraacetic acid (EDTA) caused significant suppressing effect on the uptake ofPb. Dyestuff treated rice hulls using Procion red and Procion yellow for the removal of Cr(VI), Ni(II), Cu(II), Zn(II)
