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Modified clays and clay polymer composites for immobilization of arsenic in contaminated soils

KrishiKosh

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Title Modified clays and clay polymer composites for immobilization of arsenic in contaminated soils
 
Creator Raj Mukhopadhyay
 
Subject null
 
Description t-9779
The present investigation was undertaken to study the arsenic sorption capacity by
inorganic (Ti-pillared, Fe-exchanged and phosphate-bound) and organic (ciric acid
activated, surfactant-modified and chitosan grafted) modified clays and evaluated for
immobilization potential in soils under pot culture experiments. Modified clay
products were Fe-exchanged, Ti-pillared smectite, phosphate-bound kaolinite, citric
acid activated, surfactant-modified smectite and chitosan grafted clay polymer
composites. The clay modifications for the desired properties were confirmed by
using chemical and instrumental techniques viz. XRD, FT-IR, SEM and TEM. The
arsenic adsorption-desorption on modified clay products at varying moisture and
temperature levels, the competitive adsorption of arsenic at varying level of pH onto
the screened modified clays in presence of phosphate, silicate and sulphate was
studied. Pot culture experiments were conducted with arsenic contaminated soils of
Mitrapur, West Bengal. The soils were amended with unmodified smectite, kaolinite,
Fe-exchanged smectite and phosphate-bound kaolinite applied @ 0, 1.25, 2.50 and
5.00 g kg-1 soil. Rice and spinach were used as test crops. Soils and plant samples at
two stages of crops in two consecutive years were analyzed for arsenic concentration,
transfer factor and hazard quotient.
Results indicated that modification of smectites and kaolinites resulted in
changes of interlayer space, incorporation of functional groups led to enhanced
arsenic sorption by increasing surface area. Among the modified clays, Fe-exchanged
smectite and phosphate-bound kaolinite were found most effective. At low pH (5.0),
arsenic adsorption was better. Adsorption at high temperature (40◦
C) and 2.5 cm
submergence was less onto the modified clays in soil. Adsorption was more suitable
at field capacity and 25◦
C. Phosphate was the most responsible anion for arsenic
adsorption. The order of completion is phosphate > silicate > sulphate.
The biomass yield of both the crops was increased by application of modified
clay products @ 2.50 and 5.00 g kg-1. Treatments of soils at these rates of application
also reduced available arsenic in soils and arsenic contents in plants but were
ineffective to reduce total arsenic content in soils. The soils amended with modified
clays were more efficient than the unmodified ones. Amended soils showed a
significant reduction in bioaccumulation factor of both the crops suggesting that
arsenic was efficiently immobilized in soils by modified clay products. Hazard
quotient (HQ) of rice grains and leafy parts of spinach was reduced significantly but
was above the significant risk to human health except Fe-exchanged amended soil. y
 
Date 2018-10-09T05:06:53Z
2018-10-09T05:06:53Z
2017
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/5810075021
 
Language en_US
 
Format application/pdf