Sorption of Phosphate and Cr(VI) by Fe(III) and Cr(III) Hydroxides

Abstract

Understanding the chemical behavior and interactions of Cr(VI) ( e.g., HCrO(4)(-)) and other anions, such as orthophosphate (P) with insoluble metal hydroxides ( i.e., Cr[III] and Fe[III]) in disposal landfills or in chromite ore processing residue (CORP)-enriched soil is very important in predicting the movement and the fate of Cr(VI). This study evaluates the sorption behavior of P and Cr(VI) by Fe(III) ( i.e., ferrihydrite), Cr(III) ( i.e., Cr[OH](3)), and coprecipitated Fe(III)/Cr(III) hydroxides. These metal hydroxide sorbents were synthesized, and sorption of P and Cr(VI) were conducted at different pH using a batch technology. Our results show that P and Cr(VI) sorption by metal hydroxides decreased with increasing suspension pH. Greater decrease in P sorption was observed when Cr(III) was present in the structures of hydroxides. Following the sorption of low concentration of P ( i.e., 0.5 mM), the sorption of subsequently added Cr(VI) by hydroxides was less influenced. However, Cr(VI) sorption was greatly inhibited when high concentration of P ( i.e., 10 mM) prereacted with hydroxides, particularly in Fe(III) hydroxide system. Results also indicated that high concentration of Cr(VI) (10 mM) could dissolve Cr(III) hydroxide at pH 3 and reprecipitate as an amorphous form of Cr(VI) and Cr(III) compound at pH about 6.5. Although coprecipitation of Cr(VI) with Cr(III) can inhibit Cr(VI) movement through soil profiles, the inhibition seems to be low due to the gradual release of Cr(VI) with increasing pH.

Chromium (VI) Sorption with Different Heavy Metals in Inceptisols

“…This so-called negative leaching phenomenon is easily explained by the assumption of an unequal ion distribution in the diffuse double layer, according to the Donan equilibrium and the Guoy theory (Bear, 1964). In general, in soils having higher clay content (Abollino et al, 2003), high pH (Tzou et al, 2003;Yu et al, 2003) and high CEC (Sumathi et al, 2005), sorption of Cr (VI) was less. On the other hand, in the experimental soils, though the soil pH was high, Cr (VI) sorption occurred, this being attributable to the sorption of other heavy metal cations on the soil surface, which resulted in a higher increase in the number of reactive surface groups able to complex chromate ions or in a partial neutralization of negative charge of soil colloids.…”

“…Numerous soil factors influence the dynamic equilibrium between Cr (VI) in the soil solution and the sorbed phase. Some of these factors include solution pH (Tzou et al, 2003), ionic strength (Jiewen et al, 2003), clay content (Stewart et al, 2003), competing effect of other cations (Monday and Michael, 2004), inorganic and organic ligands. Competing ions can have a marked effect on ion sorption by soils (Elliott et al, 1986).…”

Sorption Characteristics of Chromium and Its Phytotoxic Effect with or without City Compost on Maize and Spinach in a Vertisol of Central India

“…High concentration of Cr (VI) reduces its adsorption by inducing site saturation and decreasing positive interfacial potential. In the experimental soil, because of higher clay content (Abollino et al 2003), high pH (Tzou, Wang, and Loeppert 2003;Yu et al 2003), and high CEC (Sumathi, Mahimairaja, and Naidu 2005), sorption of Cr (VI) was less. It may be attributed to the fact that Cr (VI) sorption was favored by acidic conditions (Tyler and Olsson 2001).…”

Influence of inorganic anion on Cr(VI) photo-reduction in the presence of ferric ion

“…However, this technique usually leads to the accumulation of redox byproducts as coating materials or discrete solids in soil pores, resulting in a decrease of aeration or water movement in the soil profile. In addition, these by-products are amorphous and have large surface areas, which may serve as new adsorption sites for non-reducible Cr(VI) or other toxic contaminants [12]. As a result, the integral function of an ecosystem can be significantly spoiled by the addition of a great number of reductants.…”