Chitosan-g-poly(acrylic acid)-bentonite composite: a potential immobilizing agent of heavy metals in soil

Aiming to achieve heavy metal adsorption in water and soil environments, a montmorillonite rich bentonite was graft-copolymerized with chitosan, and the obtained composite material was evaluated as a metal immobilizing agent for remediating metal contaminated soil. The graft-copolymerization reaction in the composite was confirmed by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy techniques. Batch adsorption studies with varying experimental conditions, such as adsorbent amount, pH and metal concentration, were conducted to assess the metal adsorption capacity of the composite. The adsorption pattern followed the Langmuir isotherm model, and maximum monolayer capacity was 88.5, 72.9, 51.5 and 48.5 mg g−1 for Cu, Zn, Cd and Ni, respectively. Amendment of a contaminated soil with the composite enhanced the metal retention capacity by 3.4, 3.2, 4.9 and 5.6-fold for Cu, Zn, Cd and Ni, respectively, over unamended soil. The desorption percentage of metals from the composite treated soil was significantly lower than the unamended contaminated soil. The findings indicated that immobilization of heavy metals in soils could be achieved by the chitosan–bentonite, which would potentially be an inexpensive and sustainable environmental remediation technology

Impact of tillage and nutrient management practices on soil aggregate carbon pools of rice-wheat cropping system in semiarid India

207-214The soils collected from experimental site were split into two size fractions – macroaggregates (>250µm) and microaggregates (<250µm) and were used for determining the organic carbon pools in them. Results indicated that labile pools of carbon, essential to sustain soil food web, were stored mostly in macroaggregates of puddled system and microaggregates of unpuddled system. Integrated manurial treatments containing well decomposed materials were found to be better than mineral fertilizers or organic manure alone in sustaining the microbial biomass carbon content of aggregates. Improvement in stabilized pools of soil organic carbon as indicated by total polysaccharides was not proportional to the applied amount of organic manures. Aggregate binding carbon fractions like glomalin and dilute acid extractable polysaccharide in the macroaggregates of puddled system can be enhanced by application of 100% organics

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Not AvailableCommercial phosphatase enzyme (acid and alkaline) was immobilized with different nanoclays collected from three genetically different soil orders (i.e. Inceptisol, Vertisol and Alfisol) and complexes were characterized by IR spectroscopy and electron microscopy in the laboratory. Scanning electron microscopy (SEM) images showed modification of surface morphologies of nanoclay due to phosphatase adsorption (appearance of boulder like structures and rough surfaces after immobilization). IR scanning confirmed presence of characteristic band of clay mineral due to H-O-H, Si-O stretching and Al-O-H bending in all nanoclays. Nanoclay-phosphatase complexes were also characterized by means of IR and it was found that carbonyl (C=O) amide III (–CO-N–) and amide I (–CO-NH2) group present in various amino acid side chains were involved in adsorption process whereas carboxylate, primary amine and amide II (–CO-NH–) groups present in glutamine became more free on adsorption.Not Availabl

Remediation of metal contaminated soil by aluminium pillared bentonite:Synthesis, characterisation, equilibrium study and plant growth experiment

In order to enhance the efficiency of metal immobilisation, bentonite clay was pillared with polyhydroxy aluminium complexes. The pillared bentonite was systematically characterised by multiple techniques including x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The clay product was assessed for its metal removal efficiency from aqueous systems through batch experiments with variables in pH, amount of adsorbent and initial metal concentration. The adsorption data were fitted with Langmuir and Freundlich isotherm models. The maximum monolayer adsorption capacity of pillared bentonite was 61.4, 32.3 and 50.3 mg g− 1 for Cu (II), Zn (II) and Ni (II), respectively. The immobilisation efficiency of pillared bentonite was assessed by greenhouse pot culture experiment with amaranth as the test crop. Amendment of soil with pillared bentonite at 2.5% significantly improved the plant growth as well as reduced the bioavailable metals in the metal spiked soils. The study demonstrated that pillared bentonite could potentially be used for addressing heavy metal pollutions by immobilising the metals in the contaminated soil

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Not AvailableNanoclays, which are active component of soils, play a very important role for enzyme adsorption. To study the effect of nanoclays on enzyme adsorption, these were isolated from three genetically different Indian soils, i.e. black soil (Vertisols), red soil (Alfisols) and recent alluvial soil (Inceptisols). Then X-ray coherent particle sizes of different nanoclays (with and without amorphous aluminosilicates) before and after acid phosphatase adsorption were studied. Result showed that basal spacing of smectite present in nanoclays increased due to intercalation of enzyme molecules, whereas ‘d’ spacing in kaolinite did not change due to enzyme immobilization. Average particle size, calculated by Scherrer equation, increased due to enzyme immobilization for all nanoclays. In case of kaolinite, enzyme molecules acted as linkers and bind more than one particle together, which resulted in increased apparent particle size. Crystallite size of kaolinite was also more than that of mica or smectite. Increased average particle size after enzyme immobilization was confirmed from transmission electron microscopy (TEM) images.Not Availabl

Effect of waste mica on transfer factors of

A greenhouse pot culture experiment was conducted to study the effect of graded levels of waste mica (0, 10, 20 and 40 g kg-1) on reducing the radiocesium uptake by spinach (Spinacia olerecea L) and lettuce (Lactuca sativa L.) grown in 134Cs-contaminated (at 37 k Bq kg-1 soil) Inceptisols, Vertisols and Ultisols. The biomass yield, and potassium content and its uptake by crops have been significantly improved by waste mica application. The crops grown in Vertisols recorded higher biomass yield, and K content and its uptake as compared with Inceptisols and Ultisols. The average 134Cs transfer factor values recorded were : 0.21, 0.17 and 0.26 at the first cutting, 0.15, 0.12 and 0.28 at the second cutting and 0.07, 0.05 and 0.23 at the third cutting from Inceptisols, Vertisols and Ultisols, respectively. Waste mica significantly suppressed radiocesium uptake, the effect being more pronounced at 40 g mica kg-1soil. There exists an inverse relationship between the 134Cs transfer factors with plant potassium content and also the K uptake by the crop

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Not AvailableNanoclays, which are active component of soils, play a very important role for enzyme adsorption. To study the effect of nanoclays on enzyme adsorption, these were isolated from three genetically different Indian soils, i.e. black soil (Vertisols), red soil (Alfisols) and recent alluvial soil (Inceptisols). Then X-ray coherent particle sizes of different nanoclays (with and without amorphous aluminosilicates) before and after acid phosphatase adsorption were studied. Result showed that basal spacing of smectite present in nanoclays increased due to intercalation of enzyme molecules, whereas ‘d’ spacing in kaolinite did not change due to enzyme immobilization. Average particle size, calculated by Scherrer equation, increased due to enzyme immobilization for all nanoclays. In case of kaolinite, enzyme molecules acted as linkers and bind more than one particle together, which resulted in increased apparent particle size. Crystallite size of kaolinite was also more than that of mica or smectite. Increased average particle size after enzyme immobilization was confirmed from transmission electron microscopy (TEM) images.Not Availabl

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Not AvailableThe use of modified clay minerals for adsorbing arsenic (As) in contaminated soils is an underexplored area of research. The adsorption behavior of As onto inorganically modified smectite and kaolinite both in aqueous and soil media was studied. X-ray diffraction, infra-red spectroscopy, scanning and transmission electron microscopy studies confirmed successful modification of smectite through Fe-exchange and Ti-pillaring, and kaolinite through phosphate binding. The modified smectites were more efficient than phosphate-bound kaolinite in adsorbing As both in water and soil systems. Kinetic study revealed that the clay products reached adsorption equilibrium within 3 h, and the data well fitted to the power function and simple Elovich equation (R2 > 0.90). The Freundlich isotherm model best described the As adsorption data (R2 > 0.86) of the modified clay products in both the systems. The Ti-pillared smectite exhibited the highest As adsorption capacity (156.54 μg g−1 ) in the aqueous medium, while the Fe-exchanged smectite was the best material in the soil system (115.63 μg g−1 ). The partition coefficient (Kd) and adsorption efficiency (%) data also maintained the similar trend. Precipitation of As and binuclear complex formation also took place in the soil system which made the metalloid non-labile as the time passed. The inorganically modified clay products reported here hold a great potential to adsorb As in contaminated groundwater, drinking water as well as soil.Not Availabl

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Not AvailableGreenhouse experiments were conducted to assess the effect of bentonite amendment on arsenic uptake by spinach (Spinacea oleracea) cultivar Pusa Bharti. Application of bentonite to the contaminated soil increased biomass yield from 0.24(control) to 0.44 g pot-1 @ 0.25 % bentonite amended soil (T3) at first harvest and 0.65 g pot-1 @ 0.5 % bentonite amended soil (T4) after second harvest over the two years. The bioaccumulation factor (%) of arsenic varied from 13.60 in control (T1) to 3.77 (T3) in soil amended with 0.25 % bentonite at first harvest and reduced by 62.4 % in the second harvest. The hazard quotient was significantly reduced below 0.50 because of 0.25 % and 0.50 % bentonite application after first and second harvest. The arsenic concentration in plants was reduced to 0.49 mg kg-1 from 1.77 mg kg-1 in first harvest while the values were 0.50 and 1.39 mg kg-1 in 0.5 % amended and control soil, respectively after second harvest. Importantly, clay amendments effectively reduced the labile arsenic content up to 54.8 % and 58.5 % in soil during first and second harvest, respectively. Soil pH was raised significantly only in 0.5 % clay amended soil (7.89) as compared to control (6.70) after complete crop harvest. The effect of bentonite application @ 0.25 % and 0.5 % was statistically at par in most of the parameters. Hence, it may be recommended that application of bentonite @ 0.25 % may be useful to reduce the arsenic uptake by spinach as well as arsenic immobilization in polluted soil.Not Availabl

Arsenic Adsorption on Modified Clay Minerals in Contaminated Soil and Water:Impact of pH and Competitive Anions

This study evaluates the arsenic adsorption behavior of Fe-exchanged smectite and phosphate-bound kaolinite, in soil, tap water and double distilled water in the presence of competing anions such as silicate, phosphate, and sulfate, and at variable pH values. The maximum amounts of As adsorbed in soil are 620.6 and 607.6 µg g–1 at pH 5 by Fe-exchanged smectite and phosphate-bound kaolinite, respectively. The pH-modified Freundlich equation fits well (R2 > 0.96) to the adsorption data, distinguishing the effect of pH on adsorption. The coefficients of pH-value are 0.04 and 0.05 for phosphate-bound kaolinite and Fe-exchanged smectite, suggesting that low pH is suitable for the adsorption. The As adsorption is decreased in tap water at low pH compared to the soil due to the presence of iron (Fe2+/3+), sulfate, and bicarbonate in tap water. Among the competing anions in distilled water, phosphate is the most interfering anion for As adsorption. The competition coefficients of As-phosphate binary adsorption derived from the Sheindorf equation are 3.93 and 0.56 for Fe-exchanged smectite and phosphate-bound kaolinite at pH 5. The Fe-exchanged smectite can be used more effectively than phosphate-bound kaolinite for As remediation in systems having low pH (pH ≈5) and high phosphate concentration