The Kinetics of Aging and Reducing Processes of Cr(VI) in Two Soils

Abstract

To investigate the aging process and reduction of Cr(VI) in two soils. The adsorption behavior of the soils demonstrated that the paddy soil had higher adsorption capacity for Cr(VI), but the capacity was lower for Cr(III), which contrasted the results for fluro-aquic soil. The mobilizable Cr was assessed using EDTA extraction. The results suggested that the reduction of Cr(VI) to Cr(III) and the aging process occurred simultaneously. A simplified kinetic model was established and the rate constants of the reduction and aging processes were obtained. The aging process and reduction of Cr(VI) were faster in the paddy soil, due to a higher adsorption capacity and stronger reducing ability, as indicated by the organic matter and amorphous Fe oxides. The Cr(III) aging was faster in the fluro-aquic soil due to the low solubility of Cr(III) at a high pH. The modeling study provides a fundamental understanding of the dynamics of Cr mobility in a complicated soil system.

Kinetics of Chromium Reduction Associated with Varying Characteristics of Agricultural Soils

“…All R 2 values were higher than 0.45, suggesting that the Cr(VI) reduction followed first-order kinetics in the soils with p values below 0.05. Moreover, the k values in most cases of the present study were much higher than those reported in the temperate regions [20,21]. Most of the soils with low k values (<0.05 day −1 ) were subsoils derived from sandstones, slates, serpentinites, or quaternary alluvium (Soil 02, 03, 06, 08, 12, 23, 28) (Table 2), which suggests that parent materials did not directly influence the reduction of Cr.…”

“…Xiao et al further found that the rate constant significantly increased with the content of ferrous ion, clay, and the richness of the microbial population [20]. Yang et al found that kinetic of Cr(VI) reduction followed the first-order reaction in soils containing an initial concentration of 187.5 mg Cr(VI) kg −1 [21]. They also showed that the rate constant was controlled by the soil's specific surface area and pH.…”

Organic Matter Counteracts the Enhancement of Cr(III) Extractability during the Fe(II)-Catalyzed Ferrihydrite Transformation: A Nanoscale- and Molecular-Level Investigation

“…In China, paddy fields had a Cr concentration exceeding China’s soil environmental quality limits in up to 3.85% of their total area . Due to the active redox dynamics of paddy soils, Cr­(III) is generally much more abundant than Cr­(VI) in soils. − Although Cr­(III) is less mobile and toxic than Cr­(VI), excess Cr­(III) in soil has a phytotoxic effect on crop growth, which poses a threat on food security through decreasing grain yield and quality. − The cycling of Cr­(III) in the paddy soils highly affects the mobility and bioavailability of Cr in rice-soil systems as shown by the frequent reports on Cr contamination in rice grains. − However, the geochemical behavior of Cr­(III) in soils with active redox dynamics remains largely unknown.…”

Aging Process of Cadmium, Copper, and Lead under Different Temperatures and Water Contents in Two Typical Soils of China

“…Previously research reported that rapid reduction of bioavailable heavy metals often occurred within 10-20 days after adding heavy metals [20][21][22]. After that, heavy metals adsorbed on the surface of soil are further slowly fixed by micropore diffusion, cavity entrapment, occlusion in solid phases by coprecipitation, surface precipitation, and so on [23,24]. e two steps of the aging process are both affected significantly by types of heavy metals, soil properties, and circumstance conditions.…”