Selenite adsorption using leached residues generated by reduction roasting-ammonia leaching of manganese nodules.

This study was carried out to investigate the adsorption characteristics of leached manganese nodule residue (MNR), generated from the reduction roasting-ammonia leaching process, towards aqueous selenite. Physicochemical characterization revealed that the leached residue was a complex mixture of oxides of mainly manganese and iron along with MnCO(3). Adsorption studies of the water washed leached residue (wMNR) at varying the pH, selenite ion concentration, wMNR dosage, heat treatment condition indicated that selenite uptake increased with increasing pH and heat-treatment temperature of wMNR. The maximum value of selenite uptake was obtained at pH ~5.0 with wMNR heat-treated at 400°C and thereafter decreased on increasing the pH and heat-treatment temperature further. The adsorption data were best fitted by the Freundlich isotherm model. The derived monolayer selenite adsorption capacities increased from, X(m)=9.50 mg Se/g (for untreated wMNR) to 15.08 mg Se/g (for wMNR heat-treated at 400°C). The results of the studies may be useful for possible utilization of MNR as an adsorbent for the removal of selenite ions from contaminated water bodies.

Oxidative decolorization of methylene blue by leached sea-nodule residues generated by the reduction-roasting ammoniacal leaching process.

The leached residue, generated after selective extraction of Cu, Ni and Co by reductive-roasting ammoniacal leaching of sea nodules, was characterized by various physicochemical methods. The finely divided residue, containing mainly manganese carbonate/silicates and manganese (III, IV) (hydr)oxides along with iron oxides, showed a lower surface area (66.3 m2 g(-1)) than that of the parent sea nodule (130 m2 g(-1)). The catalytic efficiency of water-washed sea nodule residue (WSNR) was evaluated taking oxidative decolorization of methylene blue (MB) as the test reaction. The extent of decolorization was decreased with increase in pH but increased in the presence of H2O2 or NaCl. Decolorization of MB occurred in two consecutive steps; the rate constant of the first step was -10 times higher than that of the second step. The formation of a surface precursor complex between WSNR and MB at a rate-limiting step, followed by electron transfer from MB to the active metal centre of WSNR and release of product(s), was proposed as the decolorization process.

Enzootic calcinosis in sheep: soil-plant-animal relationship.

Chemical compositions of soil, water, feeds, and forages on a farm where sheep were affected with calcinosis (experimental site) and a farm with sheep not affected with calcinosis (control site) were determined. The study lasted 1 year. It was observed that water from the experimental site had higher electrical conductivity and calcium level than from the control site. Higher conductivity indicated greater mineral content in the water. Soil from the experimental site had lower levels of potassium, nitrogen, and phosphorus and higher content of exchangeable calcium as compared with these values of the control site. Exchangeable Ca:Mg ratio for soil of the experiemntal site was twice greater than that of the control site. Forage plants of the experimental site had lower concentrations of nitrogen, phosphorus, calcium, magnesium, and copper, but higher values of potassium and sulfur. The K:Ca + Mg, K:P, and K:Ca ratios for plants from the experimental site were higher and Ca:P ratio was lower than those of the control site. Analysis of ruminal content of the affected sheep revealed higher K:Ca + Mg, K:P, and Ca:P ratios than those of the control sheep. Due to the close relationship of metabolism of calcium, phosphorus, potassium, and magnesium, evidence of the existance of their imbalances in feeds and forages of the affected farm possibly contributing to the causation of the pathologic calcification of soft tissues of the sheep has been presented.