Methods and techniques for the selective extraction and recovery of oxoanions

Abstract

An important goal in environmental chemistry is the extraction of metals that are toxic or radioactive from soils and waters. For many such metals, the problem is solved by designing compounds with coordination sites that are specific for that particular metal. For cases such as oxoanions, however, where the inorganic center is already fully coordinated by oxygens, different strategies need to be used. Chromate, phosphate, selenate, pertechnetate, and aluminate are such anions. These species are problematic contaminants in soils and waters because they are either toxic, environmentally undesirable, or radioactive. Furthermore, under both acidic and basic conditions, the coordination positions of these oxoanions are occupied by oxygens. Chromium(VI) as either chromate or dichromate presents a particular problem because it is a strong oxidizing agent. In this review the different methods of extracting this group of pseudotetrahedral oxoanions are discussed, along with the individual advantages and limitations of each strategy.

Removal of toxic metal Cr(VI) from aqueous solutions using sawdust as adsorbent: Equilibrium, kinetics and regeneration studies

“…Because of the stricter environmental regulations, a cost effective alternate technology for the treatment of Cr(VI) contaminated wastewater is highly desired by the industries [18]. There are various treatment technologies available to remove Cr(VI) from wastewater such as chemical precipitation [19,20], ion-exchange [21,22], membrane separation [23], electrocoagulation [24], solvent extraction [25], reduction [26], reverse osmosis [25], and adsorption [16,27]. These techniques are economically expensive for the removal of Cr(VI) from wastewater.…”

Fe3+ coordinated to amino-functionalized MCM-41: an adsorbent for the toxic oxyanions with high capacity, resistibility to inhibiting anions, and reusability after a simple treatment

“…The removal of the toxic oxyanions has been achieved by coprecipitation [12][13][14][15], reverse osmometry [16], and adsorbing colloid flotation (ACF) methods [17,18]. These methods generally need large and complicated facilities due to various equipment and reagents used in a series of treatments.…”

Pyromellitic dianhydride‐modified β‐cyclodextrin microspheres for Pb(II) and Cd(II) adsorption

“…Using HCl (0.2 (mol L À1 )) as the desorption medium and desorption time as 1 h, desorption ratio was calculated using eq. (2). From the desorption experiments, it is clear that desorption ratios are very high and the average desorption percentage is obtained for Pb (96.7%) and Cd (98.2%) from triplicate measurements without losing the modified microspheres adsorption capacities significantly in three cycles.…”