改性的植物廢物吸附廢水中的重金屬離子—中英文翻譯畢業(yè)論文

1、 改性的植物廢物吸附廢水中重金屬離子目前處理廢水的方法大致分為物理法、化學(xué)法（化學(xué)沉淀、離子交換、電浮法、膜分離、反滲透、電滲、溶液萃取等）和生物吸附法(微生物吸附和植物吸附），然而物理法和化學(xué)法操作難度大，費(fèi)用高，容易產(chǎn)生二次污染，生物吸附法中植物吸附成本低，操作簡(jiǎn)單，來(lái)源廣泛，所以植物廢物吸附重廢水中金屬離子成為了科學(xué)研究的重點(diǎn)。 1重金屬?gòu)U植物廢物吸附劑的改性研究簡(jiǎn)述 1.1未處理的植物廢物吸附劑的優(yōu)缺點(diǎn)植物廢物吸附劑大多由纖維素組成，來(lái)源豐富，包含木瓜木、玉米葉、茶葉粉、白茅葉粉、香蕉葉粉、花殼顆粒、西米、椰子樹(shù)、蕨類植物、稻殼灰和印樹(shù)皮等等。植物廢物處理廢水的優(yōu)點(diǎn)包括技術(shù)簡(jiǎn)單，吸附時(shí)

2、中幾乎不需要復(fù)雜過(guò)程，有良好的吸附能力，選擇性吸附重離子，低消耗，免費(fèi)可用，容易再生，然而，未處理的植物廢物吸附劑的應(yīng)用也帶來(lái)了一些問(wèn)題，比如，低吸附效能、耗氧量（cod)、生物化學(xué)需求(bod)以及由于植物廢物中可溶性有機(jī)物釋放的有機(jī)碳(tod)的增長(zhǎng)能引起水中氧氣大量消耗，這威脅到水生生物的生命，因此在用于凈化重金屬之前，植物廢物需要處理。 1.2改性后的植物廢物吸附劑 改性后的植物廢物表現(xiàn)出對(duì)重金屬離子良好的吸附性能，稻米殼、甘蔗蔗渣、粉煤灰、鋸屑、麥糠等經(jīng)處理后，對(duì)某些重金屬離子的吸附量、吸附速率顯著提高，但用不同改性試劑處理后吸附效果不同,所以要選擇合適的改性試劑。 1.3改性的植物

3、廢物吸附劑的分類根據(jù)吸附劑分子中引入的吸附基團(tuán)的種類和吸附方式的不同，可以將吸附劑分為陽(yáng)離子吸附劑，陰離子吸附劑，兩性吸附劑，離子螯合吸附劑。 1.4改性后的植物廢物吸附劑的制備 首先用清水初洗抽濾烘干，篩篩選合適粒徑顆粒，其次使用合適的有機(jī)試劑除去植物色素、一些極性物質(zhì)，并去離子水洗滌二次洗滌，抽濾烘干，最后用礦物質(zhì)，有機(jī)酸，堿溶液，氧化劑，有機(jī)化合物等改性化學(xué)試劑處理，待備用。 2吸附機(jī)理的分析重金屬離子擴(kuò)散到表面并沉積；重金屬離子擴(kuò)散到吸附中心發(fā)生離子交換；重金屬離子與含氧官能團(tuán)發(fā)生化學(xué)吸附，如發(fā)生絡(luò)合反應(yīng)、氧化還原反應(yīng)等，溶質(zhì)從水中移向固體顆粒表面發(fā)生吸附的過(guò)程是水、溶質(zhì)和吸附劑間作用

4、的結(jié)果，發(fā)生吸附的主要原因在于溶質(zhì)對(duì)水的疏水性和溶質(zhì)對(duì)顆粒的較高親和力。植物廢物經(jīng)改性后，引入了大量的表面活性基，增強(qiáng)了吸附劑吸附能力。 3吸附效率的影響因素3.1ph值的影響 當(dāng)廢水ph值較低時(shí)，一方面h+將與目標(biāo)離子競(jìng)爭(zhēng)活性吸附位點(diǎn)，高度質(zhì)子化，目標(biāo)離子參與的活性吸附位點(diǎn)減少，從而對(duì)金屬離子的吸附量減少，ph值過(guò)高時(shí)，金屬離子將與-oh生成沉淀，處于負(fù)離子氛圍中，不利于和吸附劑發(fā)生反應(yīng)，因而需選擇最佳ph值吸附范圍。3.2溫度的影響 一般情況下，溫度對(duì)吸附的影響不大，若吸附是放熱過(guò)程，則吸附劑吸附能力隨溫度的升高而降低；若吸附是吸熱過(guò)程，則吸附劑吸附能力隨溫度的升高而升高；此外溫溫度較高時(shí)

5、隨著溶液溫度的增加其粘度降低，從而增加了溶質(zhì)分子的分散速率。吸附劑不同，吸附作用機(jī)制也各異，溫度對(duì)重金屬離子吸附量的影響也有差異。 3.3接觸時(shí)間的影響 隨時(shí)間的增加植物廢物吸附量逐漸增加，但當(dāng)?shù)竭_(dá)一定時(shí)間，吸附達(dá)到平衡，此時(shí) 植物廢物內(nèi)部孔隙都已經(jīng)達(dá)到飽和，吸附質(zhì)很難被吸附在吸附劑表面。 3.4重金屬初始濃度和吸附劑的濃度吸附效率跟重金屬初始濃度與植物廢物濃度比有關(guān)，兩者比值越大，植物廢物吸附量越大，除非達(dá)到飽和狀態(tài)。比值越大，重金屬對(duì)植物廢物表面積和活性位點(diǎn)的利用越充分，吸附效率高。 3.5其他雜質(zhì)離子的影響 在混合溶液中需要考慮其他離子對(duì)目標(biāo)離子吸附的影響，目標(biāo)離子同其他離子可能存在協(xié)同

6、，拮抗和加和作用，關(guān)鍵是否與目標(biāo)離子爭(zhēng)奪吸附位點(diǎn)，還是發(fā)生親和作用。 3.6吸附劑粒徑孔隙的影響 顆粒的比表面積和孔容越大吸附劑的吸附能力越強(qiáng)，應(yīng)篩選指定孔容和表面積的顆粒，一般以粒徑為依據(jù)篩選，此外孔隙擴(kuò)散速率是制約吸附的主要速率的主要原因，經(jīng)改性的吸附劑顆粒比表面積和孔隙結(jié)構(gòu)發(fā)生變化，進(jìn)而影響吸附劑吸附效率。 4改性的花生殼對(duì)鉻吸附情況的簡(jiǎn)述鉻離子廢液ph為1-2，接觸時(shí)間為100min、花生殼濃度與鉻離子初始濃度比為200/1，粒徑為0.25-0.5mm時(shí)吸附效率最高。 5植物廢物吸附劑的應(yīng)用改性植物廢物可廣泛應(yīng)用于吸附廢水中重金屬離子，醫(yī)藥，半導(dǎo)體應(yīng)用等，解決海洋污染和生活用水污染問(wèn)題

7、。最佳吸附劑材料和改性物質(zhì)的選擇成為研究者們研究的重點(diǎn)。 6植物廢物吸附劑的發(fā)展前景 農(nóng)林廢棄物是一種來(lái)源豐富的可再生資源，將植物廢物用于工業(yè)廢水，不僅可以降低廢水污染，而且降低廢水處理成本，為植物廢物綜合利用提供新途徑，農(nóng)林廢棄物的合理開(kāi)發(fā)利用必將帶來(lái)巨大的經(jīng)濟(jì)利益和社會(huì)效益，然而植物廢物吸附劑對(duì)重金屬吸附具有高度選擇性，所以仍需克服這一限制。河北師范大學(xué)匯華學(xué)院本科生畢業(yè)論文（設(shè)計(jì)）翻譯文章摘要：纖維質(zhì)的植物廢料可作為廉價(jià)的吸附劑除去重金屬離子，它們除去重金屬離子的性能受化學(xué)處理的影響，通常，化學(xué)改良的植物廢料與未改良的相比，能顯示出更強(qiáng)的吸附能力，這些化學(xué)修飾物包括礦物質(zhì)、有機(jī)酸、堿溶液

8、、氧化劑、有機(jī)化合物等等，這次研究了包含大米殼花粒、鋸末、甘蔗蔗渣、水果廢棄物、雜草等的植物廢料吸附劑。關(guān)鍵詞：吸附 植物廢物 廉價(jià)吸附劑 重金屬 廢水處理1介紹 由于高速發(fā)展的工業(yè)化，重金屬過(guò)量地釋放到環(huán)境中，在工業(yè)廢水中常檢測(cè)到鎘、鋅、銅、鎳、鉛、汞和鉻。這源于金屬電鍍、采礦活動(dòng)、冶煉、電池制造、印刷攝影等工業(yè)。不像有機(jī)廢物，重金屬不可降解，它們?cè)诨罱M織中積累，導(dǎo)致各種疾病和失調(diào)癥，因此必須在它們釋放前除去。研究者用廉價(jià)的吸附劑產(chǎn)品取代昂貴的，廢水處理的方法如化學(xué)沉淀、離子交換、電浮法、膜分離、反滲透、電滲、溶液萃取等正在吸引科學(xué)家的關(guān)注，吸附作用是一種物化處理方法，能有效地除去水中的重金

9、屬，許多吸附作用的研究已經(jīng)聚焦在未處理的植物廢物上，例如木瓜木、玉米葉、茶葉粉、白茅葉粉、香蕉葉粉、花殼顆粒、西米、椰子樹(shù)、蕨類植物、稻殼灰和印樹(shù)皮等等。植物廢物處理廢水的優(yōu)點(diǎn)包括技術(shù)簡(jiǎn)單，幾乎不需要復(fù)雜過(guò)程，有良好的吸附能力，選擇性吸附重離子，低消耗，免費(fèi)可用，容易再生，然而，未處理的植物廢物吸附劑的應(yīng)用也帶來(lái)了一些問(wèn)題，比如，低吸附效能，耗氧量（cod)、生物化學(xué)需求(bod)以及由于植物廢物中可溶性有機(jī)物釋放的有機(jī)碳(tod)的增長(zhǎng)能引起水中氧氣大量消耗，這威脅到水生生物的生命，因此在用于凈化重金屬之前，植物廢物需要處理。 2.化學(xué)改良的植物廢物 植物廢物的預(yù)處理能提取出可溶性有機(jī)物，增

10、強(qiáng)螯合效能，使用改良劑的不同處理方法不同，如堿性溶液（氫氧化鈣、碳酸鈉），礦物質(zhì)和有機(jī)酸溶液（鹽酸、硝酸、硫酸、酒石酸、檸檬酸、氫硫基乙酸），有機(jī)化合物（乙二胺、甲醛、氯乙醇、甲酸），氧化劑（過(guò)氧化氫）及染料（活性橙13）等，為除可溶性有機(jī)化合物，除去水溶液的顏色，增加重金屬吸附效率，許多科學(xué)家己經(jīng)研究，各種用于改良廢物的化學(xué)藥品和他們的最大吸附能力已經(jīng)展示在表格1中。2.1稻米殼稻殼是由纖維素32.24%，半纖維素21.34%，木質(zhì)素21.44%和礦物質(zhì)火山灰15.05%以及大量硅灰礦物質(zhì)（比例高達(dá)96.34%）組成，稻殼不溶于水，良好的化學(xué)穩(wěn)定性，具有較高的機(jī)械強(qiáng)度和粒狀結(jié)構(gòu)，這使它成為除

11、去廢水中重金屬良好的吸附材料，鹽酸氫氧化鈉、碳酸鈉、環(huán)氧氯丙烷和酒石酸通常用于化學(xué)處理稻米殼，預(yù)處理的稻殼能移除木質(zhì)素、半纖維素，降低纖維素結(jié)晶度，增加孔隙度或表面積,一般地，化學(xué)改良過(guò)的稻米殼比未改良的稻米殼顯示出更高的吸附能力。同時(shí)，用于處理植物廢物的大多數(shù)酸都是稀酸，如鹽酸、硫酸和硝酸。據(jù)esteghlalian蓮等。（1997）使用稀硫酸預(yù)處理能提高反應(yīng)速率和加快纖維素的水解，濃縮酸是水解纖維素的有力試劑，但是他們是有毒的，腐蝕性的，必須被還原，然而在某些情況下，鹽酸處理的稻殼對(duì)鎘吸附能力不如未處理的稻米殼，（kumar和bandyopadhyay，2006）。這由于米殼表面的吸附部位

12、將會(huì)被質(zhì)子化，重金屬無(wú)法被吸附在吸附劑表面。wong等(2003a)對(duì)各種被羧酸（檸檬酸、水楊酸、酒石酸、草酸、扁桃酸、蘋果酸和次氮基三乙酸）改性的米殼進(jìn)行了銅和鉛的吸附研究，酒石酸改良的米殼的吸附能力最高，然而酯化酒石酸改良米殼大大降低了對(duì)銅和鉛的吸收，高摩爾比的螯合劑如次氮基三乙酸和次乙亞基四乙酸（edta）對(duì)鉛的吸收具有抑制作用，為除去cr（vi）、ni（ii）、cu（ii）、zn（ii）、cd（ii）、hg（ii）和pb（ii）. 改良植物廢物作為除去水溶液中重金屬離子的吸附劑的總結(jié)suemitsu等使用紅色和黃色的普施安處理稻殼（1986）。大于80%的cd(ii)、 pb(ii)

13、和hg(ii)離子能夠被這兩種處理類型的吸附劑除去，而cr(vi)為最低的移除比例(40%)。2.2谷物渣 low等證明（2000）用氫氧化鈉處理的谷物渣能增強(qiáng)對(duì)pb(ii)和cd(ii)離子的吸附性，然而鹽酸處理過(guò)的谷物渣比未處理的吸附性要低，經(jīng)基本處理后吸附性的增加可以解釋為，因鄰甲基酯組的水解，半乳糖醛酸的含量增加所導(dǎo)致。對(duì)于重金屬吸附來(lái)說(shuō)，最佳值范圍是4-6。動(dòng)力學(xué)研究表明，重金屬吸附平衡吸附時(shí)間是120分鐘遵循偽二階模型，edta、次氮基三乙酸在摩爾比為1：1（金屬:配體）能螯合重金屬離子，大大降低了吸附能力，因此更多的重金屬離子保留在溶液中而不是被吸附(jeon and park,

14、 2005)。另一方面水楊酸稍減少了對(duì)鎘的吸附但是并沒(méi)有影響鉛的吸附。2.3甘蔗蔗渣/粉煤灰 junior等(2006)用琥珀無(wú)水石膏改良甘蔗蔗渣處理水溶液中銅，鎘和鉛，甘蔗蔗渣是由纖維素(50%),多糖(27%)和木質(zhì)素(23%)組成.這三種生物高分子的存在導(dǎo)致甘蔗蔗渣中富含羥基和酚基，化學(xué)修改這些基團(tuán)后產(chǎn)生吸附劑材料新性能，在甘蔗蔗渣中的羥基使用琥珀酐能被轉(zhuǎn)換成羧基，并和三種不同的化學(xué)物質(zhì)（主要是nahco3,乙二胺，三亞乙基四胺）反應(yīng)產(chǎn)生一些新性能的吸附材料，這些吸附材料對(duì)不同的重金屬顯示出不同的吸附能力，據(jù)發(fā)現(xiàn)用乙二胺，三亞乙基四胺處理的甘蔗蔗渣跟未處理的樣品相比含氮量顯著增加。動(dòng)力學(xué)

15、研究表明，乙二胺和三亞乙基四胺改良的甘蔗蔗渣吸附cu,cd和pb的平衡時(shí)間比用nahco3改良的吸附劑慢。可能由于在三亞乙基四胺改良甘蔗蔗渣中存在大量親核點(diǎn)，三亞基四胺改良的蔗渣是除去鎘和鉛的最好吸附劑材料，當(dāng)甘蔗蔗渣被甲醇改性時(shí)，得到的吸附劑并沒(méi)顯示出對(duì)鎘的良好吸附能力(ibrahim 等,2006). 過(guò)氧化氫是一種良好的氧化劑，用來(lái)除去吸附劑上附著的有機(jī)物質(zhì)，過(guò)氧化氫處理的甘蔗蔗渣飛塵除去鉻的時(shí)間（60min）比鉛（80min）短,等溫線研究顯示鉻最大的吸附能力比鉛的高，然而兩種金屬的最大吸附記錄值較低（鉛和鉻分別是2.5，4.35mg g-1），處理蔗渣飛塵的吸附機(jī)理沒(méi)有討論，但吸附膜

16、擴(kuò)散控制在低濃度金屬，顆粒擴(kuò)散控制在更高金屬離子濃度 3 結(jié)論 該審查顯示，化學(xué)改性植物廢料可以除去重金屬，這個(gè)研究吸引了更多科學(xué)家的關(guān)注。廣泛的低成本從化學(xué)改性植物廢料中獲得的吸附劑已經(jīng)被研究和多數(shù)研究都集中在去除重金屬離子，如鎘，銅，鉛，鋅，鎳和cr（vi ）離子。最常見(jiàn)用于化學(xué)處理植物廢物的是酸和堿?；瘜W(xué)改性植物廢料從溶液中吸附重金屬的能力差別很大，化學(xué)改性在一般提高吸附劑的吸附能力。這可能是由于在改良后較多活性結(jié)合位點(diǎn)，更好的離子交換性能，以及新的官能團(tuán)的形成有利于重金屬的吸附。雖然化學(xué)改性植物廢料可以增強(qiáng)重金屬離子的吸附，使用的化學(xué)制品的成本和維護(hù)的方法也必須考慮以生產(chǎn)“低價(jià)”的吸附

17、劑。由于吸附劑表面可能會(huì)改變吸附劑的性質(zhì)，建議對(duì)于化學(xué)改性植物廢料的任何工作，表征研究涉及表面積，孔徑大小，孔隙率研究，phzpc等都要進(jìn)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.

49、dyestuff treated rice hulls using procion red and procion yellow for the removal of cr(vi), ni(ii), cu(ii), zn(ii), cd(ii), hg(ii) and pb(ii) were studied by suemitsu et al. (1986). more than 80% of cd(ii), pb(ii) and hg(ii) ions were able to be removed by the two types of treated adsorbents, while

50、cr(vi) recorded the lowest percentage removal (40%).1.2. spent grainspent grain obtained from brewery can be used to treat pb(ii) and cd(ii) ions as demonstrated by low et al., 2000.treatment of spent grain with naoh greatly enhanced adsorption of cd(ii) and pb(ii) ions, whereas hcl treated spent gr

51、ain showed lower adsorption than the untreated spent grain. the increase in adsorption of heavy metal ions after base treatment could be explained by the increase in the amount of galactouronic acid groups after hydrolysis of o-methyl ester groups. the best ph range for metal adsorption was 6. kinet

52、ic study reveals that the equilibrium time of adsorption was 120 min for both metal ions and adsorption followed pseudo-second-order model. the maximum adsorption capacity for lead was two times higher than cadmium. the effect of organic ligands (edta, nitrilotriacetic acid and salicylic acid) on ad

53、sorption efficiency was assessed and adsorption was greatly reduced by edta and nitrilotriacetic acid at molar ratio of 1:1 (metal:ligand). edta and nitrilotriacetic acid could chelate the heavy metal ions, therefore more metal ions would remain in the solutions rather than being adsorbed (jeon and

54、park, 2005). salicylic acid on the other hand slightly reduced the percentage of cadmium adsorption but did not affect adsorption of lead.1.3. sugarcane bagasse/fly ashjunior et al. (2006) reported the use of succinic anhydride modified sugarcane bagasse for treatment of cu, cd and pb from aqueous s

55、olutions. sugarcane bagasse consists of cellulose (50%), polyoses (27%) and lignin (23%). the presence of these three biological polymers causes sugarcane bagasse rich in hydroxyl and phenolic groups and these groups can be modified chemically to produce adsorbent materials with new properties. the

56、authors reported that the hydroxyl groups in sugarcane bagasse could be converted to carboxylic groups by using succinic anhydride. the carboxylic groups were later reacted with three different chemicals mainly nahco3, ethylenediamine and triethylenetetramine to produce new properties of adsorbent m

57、aterials which showed different adsorption capacities for metal ions. it was found that sugarcane bagasse treated with ethylenediamine and triethylenetetra- mine shows a remarkable increase in nitrogen content compared to untreated sample, and triethylenetetramine modified sugarcane bagasse has a hi

58、gher increasing extent. the presence of amide group was also detected in ethylene- diamine and triethylenetetramine modified sugarcane bagasses as a result of the reaction between -cooh and - nh2 groups. kinetic studies showed that equilibrium time for adsorption of cu, cd and pb onto tethylenediamine and triethylenetetramine modified sugarcane bagasses were slower than that for adsorbent modified with nahco3. triethylenetetramine modified su