agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions – a review

1、ReviewAgricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions – A reviewDhiraj Sud *, Garima Mahajan, M.P. KaurSant Longowal Institute of Engineering and Technology, De

2、partment of Chemistry, Longowal 148106, IndiaReceived 15 October 2007; received in revised form 22 November 2007; accepted 22 November 2007 Available online 14 February 2008AbstractHeavy metal remediation of aqueous stre

3、ams is of special concern due to recalcitrant and persistency of heavy metals in environment. Conventional treatment technologies for the removal of these toxic heavy metals are not economical and further generate huge q

4、uantity of toxic chemical sludge. Biosorption is emerging as a potential alternative to the existing conventional technologies for the removal and/ or recovery of metal ions from aqueous solutions. The major advantages o

5、f biosorption over conventional treatment methods include: low cost, high efficiency, minimization of chemical or biological sludge, regeneration of biosorbents and possibility of metal recovery. Cellulosic agricultural

6、waste materials are an abundant source for significant metal biosorption. The functional groups present in agri- cultural waste biomass viz. acetamido, alcoholic, carbonyl, phenolic, amido, amino, sulphydryl groups etc.

7、have affinity for heavy metal ions to form metal complexes or chelates. The mechanism of biosorption process includes chemisorption, complexation, adsorption on surface, diffusion through pores and ion exchange etc. The

8、purpose of this review article is to provide the scattered available information on various aspects of utilization of the agricultural waste materials for heavy metal removal. Agricultural waste material being highly eff

9、icient, low cost and renewable source of biomass can be exploited for heavy metal remediation. Further these biosorbents can be mod- ified for better efficiency and multiple reuses to enhance their applicability at indus

10、trial scale. ? 2007 Elsevier Ltd. All rights reserved.Keywords: Agricultural wastes; Biosorption; Industrial effluents; Heavy metal remediation; Adsorbent1. IntroductionToxic heavy metal ions get introduced to the aquati

11、c streams by means of various industrial activities viz. min- ing, refining ores, fertilizer industries, tanneries, batteries, paper industries, pesticides etc. and posses a serious threat to environment (Celik and Demir

12、bas, 2005; Friedman and Waiss, 1972; Kjellstrom et al., 1977; Pastircakova, 2004). The major toxic metal ions hazardous to humans as well as other forms of life are Cr, Fe, Se, V, Cu, Co, Ni, Cd, Hg, As, Pb, Zn etc. Thes

13、e heavy metals are of specific con- cern due to their toxicity, bio-accumulation tendency and persistency in nature (Friberg and Elinder, 1985; Garget al., 2007; Randall et al., 1974). Several past disasters due to the c

14、ontamination of heavy metals in aquatic streams are Minamata tragedy in Japan due to methyl mer- cury contamination and ‘‘Itai-Itai” due to contamination of cadmium in Jintsu river of japan (Friberg and Elinder, 1985; Kj

15、ellstrom et al., 1977). Various regulatory bodies have set the maximum prescribed limits for the discharge of toxic heavy metals in the aquatic systems. However the metal ions are being added to the water stream at a muc

16、h higher concentration than the prescribed limits by industrial activities, thus leading to the health hazards and environmental degradation (Table 1). Conventional methods for removal of metal ions from aqueous solution

17、s include chemical precipitation, ion exchangers, chemical oxidation/reduction, reverse osmosis, electro dialysis, ultra filtration etc (Gardea-Torresdey et al., 1998; Patterson, 1985; Zhang et al., 1998). However these0

18、960-8524/$ - see front matter ? 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.11.064* Corresponding author. Tel.: +91 1672 284698; fax: +91 1672 284840. E-mail address: suddhiraj@yahoo.com (D. Sud).

19、Available online at www.sciencedirect.comBioresource Technology 99 (2008) 6017–6027involves a solid phase (sorbent) and a liquid phase (solvent) containing a dissolved species to be sorbed. Due to high affinity of the so

20、rbent for the metal ion species, the latter is attracted and bound by rather complex process affected by several mechanisms involving chemisorption, complexa- tion, adsorption on surface and pores, ion exchange, chela- t

21、ion, adsorption by physical forces, entrapment in inter and intrafibrillar capillaries and spaces of the structural poly- saccharides network as a result of the concentration gradi- ent and diffusion through cell wall an

22、d membrane (Basso et al., 2002; Sarkanen and Ludwig, 1971; Qaiser et al., 2007) (Fig. 1). Agricultural waste materials are usually composed of lignin and cellulose as the main constituents. Other compo- nents are hemicel

23、lulose, extractives, lipids, proteins, simple sugars, starches, water, hydrocarbons, ash and many more compounds that contain a variety of functional groups present in the binding process. Cellulose is a crystalline homo

24、-polymer of glucose with b1 ? 4 glycosidic linkageand intra-molecular and intermolecular hydrogen bonds (Demirbas, 2000a,b). Hemicellulose is a heteropolymer of mainly xylose with b1 ? 4 glycosidic linkage with other sub

25、stances of acetyl feruoyl and glycouronyl groups (Garg et al., in press). Lignin is three dimensional polymer of aro- matic compounds covalently linked with xylans in hard- woods and galactoglucomannans in softwoods (Gar

26、g et al., 2007; Sjo ¨tro ¨m, 1981) The functional groups present in biomass molecules acetamido groups, carbonyl, pheno- lic, structural polysaccharides, amido, amino, sulphydryl carboxyl groups alcohols and es

27、ters (Beveridge and Mur- ray, 1980; Gupta and Ali, 2000). These groups have the affinity for metal complexation. Some biosorbents are non-selective and bind to a wide range of heavy metals with no specific priority, wher

28、eas others are specific for certain types of metals depending upon their chemical composi- tion. The presence of various functional groups and their complexation with heavy metals during biosorption pro- cess has been re

29、ported by different research workers usingBEn+ - Biomolecules with Exchangeable ions BL-binding sites of biomass Mn+- Metal ions. BM n+ - Biomolecules with metal ions M+ TTRANSPORTAGRICULTURAL WASTEBIOMASS FUN

30、CTIONAL GROUPS -COOH, -NH2, -OH, - CONH2 3BEn+ Mn+BM n+ E n+ION EXCHANGE M nBLM (BL) nM +SURFACE ADSORPTIONM+ M+DIFFUSION M+M+ TM+COMPLEXATION & CHELATION M+MS MOHPRECIPITATION , -SH, -OCHFig. 1. Plausible mech