A Review on Cr(VI) Adsorption Using Inorganic Materials

Abstract

Chromium compounds are widely used in electroplating, metal finishing, magnetic tapes, pigments, leather tanning, wood protection and electronic and electrical equipment. Hexavalent chromium is a highly toxic metal and produces health damages. The most soluble, mobile and toxic forms of hexavalent chromium in soils are chromate and dichromate and the chromium distribution is also controlled by redox processes, its adsorption decreases with increasing pH and when competing dissolved anions are present. Several techniques have been developed to remove Cr(VI) from wastewater but these techniques have disadvantages such as high cost, non-selective, pH dependence, etc. The use of low cost sorbents has been investigated as a replacement for current costly methods; natural materials with a high adsorption capacity for heavy metals can be obtained. Modification of the sorbents can improve adsorption capacity. This paper includes some techniques for remove Cr(VI) with clays, silica and zeolites from aqueous solutions, some of the treated adsorbents show good adsorption capacities.

Fractionation Behavior of Chromium Isotopes during the Sorption of Cr (VI) on Kaolin and its Implications for Using Black Shales as a Paleoredox Archive

“…We therefore hypothesize that the initial 0.5M HCl leach likely recovered the electrostatically bound Cr. As metal sorption on kaolinite is mainly limited to the surface (Rosales‐Landeros et al, ) and as the mq solution does not support significant surface precipitation due to a limited ion availability, the 6M HCl leach likely mobilized Cr bound to sorption sites of lower reactivity.…”

“…The kaolin (china clay) used in this study was provided by English China Clays and was mined in the open pits at Saint Austell in Cornwall, United Kingdom. Kaolin was chosen as the adsorbing material to constrain the sorption experiments to surface processes, as kaolinite's sorption and exchange capacity is primarily confined to the surface, in contrast to other clays, such as smectite or illite, where sorption processes also involve interior lattice exchange site reactions (Rosales‐Landeros et al, ). A piece of kaolin was powdered using an agate mortar and pestle and washed three times with 6M HCl in order to enhance surface reactivity.…”

“…Clay minerals can remove pollutants from solution through adsorption mechanisms and cation exchange (Acharya et al, 2017;Bhattacharyya & Sen Gupta, 2006;Rosales-Landeros et al, 2013). They are very fine particles that have the chemical properties of colloids (Sharma et al, 2009), and their high chemical and mechanical stability, high specific surface area, and consequential high cation exchange capacity make them excellent adsorbents (Ajouyed et al, 2011;Bhattacharyya & Sen Gupta, 2006).…”

Low-temperature plasma-modified zeolite (LTPMZ) vs. natural Bulgarian zeolite (NBZ) – Comparative physicochemical, UV/VIS and FTIR studies

“…The silanol groups can be isolated (free silanol groups), where the surface silicon atom has three bonds into the bulk structure and the fourth to OH-group and the vicinal or bridged silanols, where two isolated silanol groups attached to two different silicon atoms are bridged by Hbond. A third type of silanols, called geminal silanols, consist of two hydroxyl groups attached to one silicon atom [15]. Geminal silanols are close enough to have H-bonds, whereas free silanols are too far apart, as indicated in Figure 12.…”

Photocatalytic Degradation of Salicylic Acid and Reduction of Cr(VI) using TiO2

“…In aquatic environments, chromium exists mostly in the hexavalent chromium Cr(VI) and trivalent chromium Cr(III) states. Anionic Cr(VI) is far more mobile and toxic than Cr(III) and more difficult to remove from water [7]- [8]. Similar to many other metal cations, however, aqueous Cr(III) can be readily precipitated as Cr(OH) 3 or removed by adsorption and ion exchange.…”