Study on the characteristics of Cd2+ adsorption of mineral processing wastewater by micro-organisms supported by hydrothermal carbon

With the development of science and technology and the improvement of human living standards, gold has been widely used in various industries, but with the mining of gold mines, a large number of mineral processing wastewater rich in heavy metal ions has caused damage to the environment. Especially the heavy metal cadmium (Cd), because of its strong biological toxicity and high enrichment seriously harm human health and ecological safety. Therefore, in order to effectively control cadmium pollution in gold mine wastewater, based on immobilized microbial technology, this study used the concentration gradient method of heavy metals to screen the in situ dominant bacteria with strong tolerance to Cd2+ from the sludge of gold mine wastewater pool, and used hydrothermal carbon as the immobilized carrier. The immobilized microbial activated carbon spheres (HC-PVA-SA-MOI) were prepared by a composite fixation method combining adsorption-embedding and cross-linking. The microscopic morphology, elemental composition, surface functional groups, specific surface area and porosity of HC-PVA-SA-MOI were analyzed by SEM, XPS and BET characterization experiments. The results showed that HC-PVA-SA-MOI was spherical in uniform size, mainly composed of C, O, N, Na and other elements. The specific surface area was 134.1821 m2/g, and the in-situ dominant strains were successfully attached to the surface of hydrothermal carbon. The effects of pH, adsorption time, temperature, initial concentration, dosage of adsorbent and coexisting ions on the adsorption performance of HC-PVA-SA-MOI were studied through the optimization experiment of adsorption conditions. The results showed that when the initial concentration of Cd2+ was 100 mg/L, the dosage of HC-PVA-SA-MOI was 5 g/L, and the pH of the solution was 6. When the adsorption time is 48 h and the temperature is 30 ℃, the best adsorption conditions are HC-PVA-SA-MOI, and the removal rate of Cd2+ is 98.59%. In addition, the adsorption kinetics experiment and adsorption isotherm model experiment found that the adsorption of Cd2+ by HC-PVA-SA-MOI was more consistent with the quasi-second-order kinetic model and Langmuir model, indicating that the adsorption mechanism of Cd2+ by HC-PVA-SA-MOI was mainly homogeneous monolayer chemisorption. The analysis of microbial diversity and subcellular structure showed that Halomonas played the main role in the adsorption of Cd2+, and the main role of microbial structure was cell wall and cell membrane. The results show that the removal rate of Cd2+ in wastewater by HC-PVA-SA-MOI can still reach 90.11% after 5 sorption-desorption cycles, which has good reuse performance. Based on its sustainability, low cost and excellent adsorption properties, HC-PVA-SA-MOI is expected to be used as an adsorbent for the practical treatment of Cd2+ in gold mine wastewater.