No abstract

Soil microorganisms and soil enzyme activities are important indexes to evaluate soil status. The soil pollution status was evaluated by measuring the physical and chemical properties and heavy metal content of rare earth combined contaminated soil around the Maoniuping old mining area and tailings ponds in different seasons, and measuring the number and diversity of microorganisms and the soil enzyme activities of the arable soil microecology. This research shows that the physical and chemical properties of farmland soil in old mining areas and tailings ponds in different seasons are significantly different, the concentration of rare earth combined contamination in old mines is greater than that in the tailings area, and the changes in the concentration of rare earth combined contamination cause significant changes in soil microecology. Rare earth combined contamination inhibits fungal and bacterial vital activities and promotes the growth of actinomycetes; reduces the sensitivity of sucrase to heavy metal contamination, promotes the activity of phosphatase, and the effect on urease is that of “promotion at low concentration and inhibition at high concentration”; and reduces the community’s ability to use carbon sources and, as a result, the community species are rare and distributed unevenly and the community structure is simple. These results indicate that rare earth combined contamination is potentially harmful to soil microorganisms, which can provide a theoretical basis for the ecological restoration of farmland soil in mining areas.

Measured CeFn (n=1, 2, 3) complexation constant and solubility product constant of CeF4 and Na2CeF6 by ICP-AES and UV spectrophotometer, when Ce4+ and F− complexation reaction in water medium and nitric acid medium respectively, and the effects of Re3+and nitric acid concentration on Ce4+ and F− complexation reaction were studied. The experimental results show that the first-order complexation constant of Ce4+ and F− is CeF3 +=6.94*106, the second-order complexation constant is CeF2 2+=4.541*1011, and the third-order complexation constant is CeF3 +=6.232*1014. Compared with the complexation reaction of Ce4+ and F− in water medium and nitric acid medium, the complexation reaction of Ce4+ and F− in nitric acid medium is better. Re3+ appears, which affects the complexation reaction between Ce4+ and F−. When in nitric acid medium, the higher the concentration of nitric acid, the more unfavorable the complexation of Ce4+ and F−. The study of the relevant physical constants of Ce4+ and F− in this paper can be helpful for the separation of Ce4+ and F−, enrich the physical and chemical information of rare earth elements, and provide the basic theoretical basis for the rare earth fluoride that is difficult to be separated and recovered from the tailings, so as to reduce the harm to the soil environment.

In order to improve the removal efficiency of refractory organic matters in micro-polluted source water, biological manganese oxides (BMOs) were generated in situ in the biological aerated filter (BAF) (BAF 2#), which could oxidize the refractory organic matters into biodegradable organic matters. CODMn and NH4+-N in the effluent of BAF 2# both stabilized on the 39th day, while CODMn and NH4+-N in the effluent of the control BAF (BAF 1#) stabilized on the 38th and 42nd days, respectively. In the steady phase, the removal rates of CODMn and NH4+-N in BAF 1# were 41.51% and 94.79%, respectively, while in BAF 2#, they were 54.52% and 95.55%, respectively. BMOs generated in BAF 2# evidently improved the efficiency of CODMn removal. With the increase in the influent Mn2+ in BAF 2#, the rate of CODMn removal was gradually improved to 63.60%, while the efficiency of NH4+-N removal was slightly improved, CODMn was evidently removed in each section of the filter layer, and ammonia was mainly removed in the 0~0.8 m layer of the filter. CODMn was evidently removed in each section of the filter layer, and NH4+-N was mainly removed in the 0~0.8 m layers of the filter. Biological CODMn, Mn2+, and NH4+-N removal all followed the first-order kinetic reaction. As the influent Mn2+ gradually increased from 0 to about 0.5, 1, and 2 mg/L, the efficiency of CODMn removal along the filter layer was significantly improved, but the efficiency of NH4+-N removal was slightly improved. The kinetic constant k of biological CODMn removal significantly increased, while the kinetic constant k of biological Mn2+ and NH4+-N removal gradually increased.