Species identification and mutation breeding of silicon-activating bacteria isolated from electrolytic manganese residue

Enhanced green remediation and refinement disposal of electrolytic manganese residue using air-jet milling and horizontal-shaking leaching

The reclamation and reuse of electrolytic manganese residue (EMR) as a bulk hazard solid waste are limited by its residual ammonia nitrogen (NH4+-N) and manganese (Mn2+). This work adopts a co-processing strategy comprising air-jet milling (AJM) and horizontal-shaking leaching (HSL) for refining and leaching disposal of NH4+-N and Mn2+ in EMR. Results indicate that the co-use of AJM and HSL could significantly enhance the leaching of NH4+-N and Mn2+ in EMR. Under optimal milling conditions (50 Hz frequency, 10 min milling time, 12 h oscillation time, 400 rpm rate, 30 ℃ temperature, and solid-to-liquid ratio of 1:30), NH4+-N and Mn2+ leaching efficiencies were optimized to 96.73% and 97.35%, respectively, while the fineness of EMR was refined to 1.78 µm. The leaching efficiencies of NH4+-N and Mn2+ were 58.83% and 46.96% higher than those attained without AJM processing. The AJM used strong airflow to give necessary kinetic energy to EMR particles, which then collided and sifted to become refined particles. The AJM disposal converted kinetic energy into heat energy upon particle collisions, causing EMR phase transformation, and particularly hydrated sulfate dehydration. The work provides a fire-new and high-efficiency method for significantly and simply leaching NH4+-N and Mn2+ from EMR.

A review of metallurgical slags as catalysts in advanced oxidation processes for removal of refractory organic pollutants in wastewater

With the rapid growth of the metallurgical industry, there is a significant increase in the production of metallurgical slags. The waste slags pose significant challenges for their disposal because of complex compositions, low utilization rates, and environmental toxicity. One promising approach is to utilize metallurgical slags as catalysts for treatment of refractory organic pollutants in wastewater through advanced oxidation processes (AOPs), achieving the objective of "treating waste with waste". This work provides a literature review of the source, production, and chemical composition of metallurgical slags, including steel slag, copper slag, electrolytic manganese residue, and red mud. It emphasizes the modification methods of metallurgical slags as catalysts and the application in AOPs for degradation of refractory organic pollutants. The reaction conditions, catalytic performance, and degradation mechanisms of organic pollutants using metallurgical slags are summarized. Studies have proved the feasibility of using metallurgical slags as catalysts for removing various pollutants by AOPs. The catalytic performance was significantly influenced by slags-derived catalysts, catalyst modification, and process factors. Future research should focus on addressing the safety and stability of catalysts, developing green and efficient modification methods, enhancing degradation efficiency, and implementing large-scale treatment of real wastewater. This work offers insights into the resource utilization of metallurgical slags and pollutant degradation in wastewater.

Optimization of Environmental Conditions for Microbial Stabilization of Uranium Tailings, and the Microbial Community Response

Uranium pollution in tailings and its decay products is a global environmental problem. It is of great significance to use economical and efficient technologies to remediate uranium-contaminated soil. In this study, the effects of pH, temperature, and inoculation volume on stabilization efficiency and microbial community response of uranium tailings were investigated by a single-factor batch experiment in the remediation process by mixed sulfate-reducing bacteria (SRB) and phosphate-solubilizing bacteria (PSB, Pantoea sp. grinm-12). The results showed that the optimal parameters of microbial stabilization by mixed SRB-PSB were pH of 5.0, temperature of 25°C, and inoculation volume of 10%. Under the optimal conditions, the uranium in uranium tailings presented a tendency to transform from the acid-soluble state to residual state. In addition, the introduction of exogenous SRB-PSB can significantly increase the richness and diversity of endogenous microorganisms, effectively maintain the reductive environment for the microbial stabilization system, and promote the growth of functional microorganisms, such as sulfate-reducing bacteria (Desulfosporosinus and Desulfovibrio) and iron-reducing bacteria (Geobacter and Sedimentibacter). Finally, PCoA and CCA analyses showed that temperature and inoculation volume had significant effects on microbial community structure, and the influence order of the three environmental factors is as follows: inoculation volume > temperature > pH. The outcomes of this study provide theoretical support for the control of uranium in uranium-contaminated sites.

Screening of silicon-activating bacteria and the activation mechanism of silicon in electrolytic manganese residue

Electrolytic manganese residue (EMR) is a kind of solid waste with a high silicon content. Most of the silicon in EMR, however, exist in the state of SiO₂, which cannot be directly absorbed by plants. Currently, it is very challenge to recover the silicon from EMR. In this study, a preliminary screening of strains with silicon-activating ability was conducted, and four strains were screened out and isolated from the soil around the tailings pond of EMR. Then, single factor experiments were conducted to obtain the optimal growth conditions of the four strains, and the results indicated that the Ochrobactrum sp. T-07 had the best silicon-activating ability from EMR after nitrosoguanidine mutagenesis (Ochrobactrum sp. T-07-B). The available silicon (in terms of SiO₂) in the leaching solution was up to 123.88 mg L^-1, which was significantly higher than that produced by Bacillus circulans and Paenibacillus mucilaginosus, the two commercial available pure culture strains. Results of direct/indirect contact experiments between Ochrobactrum sp. T-07-B and EMR revealed that bioleaching was promoted under the synergistic effect of bacteria growth on the surface of and metabolism within EMR. The newly isolated strains with silicon-activating effect are different from the existing-known silicate bacteria and may be used for more efficient silicon activation in silicate minerals.