Kinetics Of Reductive Dissolution Research Articles

Reductive Dissolution of Ferric Iron in Laterite Overburden Using Acidithiobacillus Spp. and Neutrophilic Iron-Reducing Consortia

Cuba is considered as one of the top world producer of nickel and cobalt. The laterite ore containing nickel and cobalt is mined after first removing an overburden of a long strip of soil and rock. The laterite has a high content of iron oxide (63%), which has to be removed in order to recover the nickel and cobalt. This study reports on the kinetics of reductive dissolution of the Fe(III) from the overburden by two native neutrophilic iron-reducing consortia as well as Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. All of the organisms mobilized the ferric iron in the laterite by reducing it to Fe(II). The AeRD process using At. thiooxidans was far more efficient in extracting total iron than the AnRD process using At. ferrooxidans.

Kinetics of Reductive Dissolution of Manganese Dioxide in Aqueous Formic Acid at 298 K

Kinetics of Reductive Dissolution of Manganese Dioxide in Aqueous Formic Acid at 298 K

Reductive dissolution of arsenic-bearing ferrihydrite

Ferrihydrites were prepared by coprecipitation (COP) or adsorption (ADS) of arsenate, and the products were characterized using solid-state methods. In addition, the kinetics of reductive dissolution by hydroquinone of these well-characterized materials were quantified. Characterization and magnetism results indicate that the 10 wt% As COP ferrihydrite is less crystalline and possibly has smaller crystallite size than the other ferrihydrites, which all have similar crystallinity and particle size. The results from reductive dissolution experiments show similar reaction rates, reaction mechanism, and activation energy for ferrihydrite precipitated with or without added arsenate. However, a marked decrease in reactivity was observed for 10 wt% As ADS ferrihydrite. The decrease is not attributed to differences in activation energy but rather the preferential blocking of active sites on the ferrihydrite surface. Results demonstrate that arsenic may be released by the reductive dissolution of arsenic-bearing ferrihydrite regardless of whether the arsenic is coprecipitated with or adsorbed onto the ferrihydrite. However, under these reaction conditions, release from materials with adsorbed arsenate greatly exceeds that from materials with coprecipitated arsenate. In fact, a considerable amount of arsenic was released from the 10 wt% ADS ferrihydrite before reductive dissolution was initiated. Therefore, the characterization of arsenate-bearing iron oxide materials to determine the method of arsenate incorporation into structures—perhaps by quantification of Fe–Fe coordination with EXAFS spectroscopy—may lead to improved predictions of the large-scale release of arsenic within aquifer systems under reducing conditions.