Biomethylation of arsenic is usually considered as a detoxification of arsenic because toxicity of most organic methylated arsenic is much less than that of inorganic arsenic. We investigated the feasibility of a novel bioremediation using an arsenic methylating bacterium. An arsenic methylating bacterium Bacillus cereus strain R2, isolated from soil in Miyazaki, was evaluated for growth characteristics and arsenic metabolism. The growth of strain R2 was inhibited in 50.0 mg As/l arsenic medium. Strain R2 metabolized arsenite (<5.0 mg As/l) to nonvolatile species such as monomethylarsonic acid, dimethylarsinic acid and trimethylarsenic oxide effectively. The percentage of organic methylated arsenic excreted into the medium by strain R2 showed 89.0% of total arsenic compounds when strain R2 was cultured aerobically in the medium containing 0.1 mg As/l of arsenite and 1.0 g/l of glucose for four days.
In order to investigate the heat-degradation of AS resin upon heat-process cycling, several kinds of heat-treated AS samples were prepared by using a hot-pressing or a single-screw extruder, and then, their chemical and/or physical properties were examined. From the results of FT-IR spectrum, it was found that the absorption of C = O group were measured and its intensity increased with heat-process cycles. Such an absorption peak, however, cannot be observed on the samples treated in N2. The molecular weight of the samples decreased with annealing time, and their decline ratios were increased by rising the heat-process temperature. At the same temperature, the molecular weight decline ratios depended only on the heat-process cycle numbers, and not change in spite of the screw speed of the extruder. In N2 atmosphere, however, the molecular weight decline ratios were suppressed about 50% to be compared with that in the air. Although Young’s modulus (E) obtained by stress-strain curves for the heat-process cycled AS samples with their molecular weight (Mw) more than 10,000 were almost the same, the values of E for the heat-recycled AS samples with Mw less than 10,000 decreased with its molecular weight.
Leaching of platinum (Pt) traces from Cobalt-Rich Crust (CRC) in hydrochloric acid (HCl) solution with hydrogen peroxide (H2O2) was carried out in this work. Two kinds of CRC samples with different Pt grades were used and the effects of HCl and H2O2 concentration, leaching temperature and time as well as solid-liquid ratio were investigated to evaluate the Pt leaching. The results showed that more than 95% of Pt in the CRC sample was leached out in HCl solution which concentration was more than 2 mol/L. The leaching temperature was higher than 50°C and the time was longer than 30 min whereas the solid-liquid ratio was less than 50 g/L. Similar results were observed when using HCl solution of more than 0.5 mol/L with the addition of more than 1 vol.% H2O2, while the leaching temperature was kept at 30°C and the time was longer than 15 min but at a reduced solid-liquid ratio (i.e. less than 10 g/L). There was no difference on Pt leached fraction between the two CRC samples with different Pt grades.