Assessment of electrokinetic removal of heavy metals from soils by sequential extraction analysis

Assessment of heavy metal speciation in soils impacted with crude oil in the Niger Delta, Nigeria

“…The low solubility of chromium in the soil types was probably controlled by the fact that Cr(III) forms poorly soluble hydroxocomplexes, whereas Cr(VI) form oxyanions such as CrO 4 2 À and Cr 2 O 7 2 À and adsorbed minimally to negative charged soil particles. As the pH decreases, reversal of soil solids may occur, thus increasing the adsorption of Cr(VI) on the soil surface (Reddy et al, 2001). About 10 -28% of Cr was found in the hydroxylamine chloride extractable fraction in all sites and depths.…”

The Use of Sequential Extraction Procedures for the Characterization and Management of Contaminated Soils

“…Reddy et al 34 applied electrokinetic remediation to soils contaminated by chromium, and found that the extent of migration of the metals towards the electrodes depended on their mobility, with higher migration occurring when the contaminant existed in exchangeable form. They observed low migration rates as a result of contaminants existing as non mobile complexes of precipitates.…”

“…The original designations of the five fractions obtained with Tessier's procedure are somewhat vague and may not apply to contaminated soils. For this matrix, the definitions developed by Reddy et al 34 may be more suitable: i) first fraction: loosely held contaminants, including the exchangeable and soluble forms, that can be readily extracted; ii) second fraction: tightly adsorbed contaminants and those associated with carbonates and easily soluble oxides/hydroxides under slightly acidic conditions; iii) third fraction: additional soluble metal oxides/hydroxides at slightly acidic pH as well as contaminants associated with Fe-Mn oxides; iv) fourth fraction: contaminants associated with easily oxidizable solids or compounds, including organic matter; v) fifth fraction: contaminants present as consolidated oxides, co-precipitated and strongly held complexes.…”

Biosorption and Chemical Precipitation of Lead Using Biomaterials, Molecular Sieves, and Chlorides, Carbonates, and Sulfates of Na & Ca

“…Chronic exposure to these heavy metals poses a major threat to soil, water, and food safety because of their inherent toxicity to living organisms, especially humans [2]. Several methods that have been proposed for the removal of these heavy metals from the soil, and water include adsorption and chemical precipitation [3][4][5][6][7], Lime treatment [8], ion exchange [9,10], extraction [11] and a host of other techniques delineated in Zvinowanda's paper [12]. In as much as these methods which have great potential for heavy metal remediation, they are expensive and they (a) require large amount of reagents (b) generate large volumes of reagents and (c) need further treatment of their waste and (d) may lead to incomplete mitigation and expensive waste disposal.…”