Bioleaching of effective silicon represents a crucial method for the green and efficient utilization of coal tailings (CTs). However, the influence of heavy metals present in coal tailings on this process cannot be underestimated. This study investigates the effects of five high-concentration heavy metal elements (Pb, Zn, Cu, Cr, and Ni) in CTs on the biological characteristics and leaching processes of Bacillus mucilaginosus ( B.M. ). The results indicated that varying concentrations of heavy metal elements significantly influenced the bioleaching of effective silicon by B.M. . Kinetic analysis revealed that the leaching process predominantly adhered to a chemical reaction-controlled mechanism. Changes in the functional groups, mineral composition, and morphology of the CTs surface demonstrated that chromium and nickel exerted a negligible effect on leaching effectiveness, with effective silicon concentrations of 315.71 mg/L and 322.62 mg/L, respectively. The activity of B.M. induced surface erosion of CTs, disrupting the crystal structure of silicon-bearing minerals and facilitating the conversion of silicon in quartz and kaolinite to effective silicon. In contrast, lead, zinc, and copper significantly inhibited B.M. , hindering effective erosion of CTs and resulting in lower effective silicon leaching concentrations of 129.65 mg/L, 142.68 mg/L, and 135.70 mg/L, respectively. Therefore, this study summarizes the effects of various heavy metal elements on the bioleaching of effective silicon by B.M. , providing a scientific foundation for the environmentally sustainable utilization of CTs.
Huixin Zhou,Dingxun Ma,Lingwen Dai,Lage Wuri,Yichao Wang,Xiaozhen Liu,Xinqian Shu
Coal gangue (CG) provides an abundant source of siliceous minerals that can be converted into effective silica. This study aimed to gain a deeper understanding of the evolutionary mechanism of quartz (Qtz) and kaolinite (Kln), in the conversion process of thermal–chemical coupled activation to effective silica. The structure transformation of two types of siliceous minerals and thermodynamic calculation were used to develop a phase diagram model for the formation of effective silica, and then provide a scientific basis for the thermodynamic study of solid-phase reactions. We showed that K 2 CO 3 outperformed CaCO 3 in activation efficiency in the thermal–chemical coupled activation process, and Kln had a higher activation efficiency than Qtz. Notably, when the calcination temperature reaches 850 °C, the activation efficiency of the Kln system with added K 2 CO 3 could exceed 50 %. Characterization and analysis of the effective silica properties and structure revealed that low bioactivity effective silica existed in the minerals with (K, Ca) x Si y O z , corresponding to the Q 3 structure; while high bioactivity effective silica existed in the minerals with (K, Ca) x Al w Si y O z , corresponding to the Q 3 (1Al) structure. Finally, we used FactSage thermodynamic calculation software to further predict the phase transformation process of the solid-phase reaction. The simulation results highly matched the experimental data, providing strong support for effective silica synthesis and process optimization. This study provides theoretical basis for understanding the multi-pathway, multi-phase reaction mechanisms of siliceous minerals transforming into effective silica within CG.
Yang Liu,Lixun Zhang,Zhengfang Zhang,Ying Zhang,Yuntao Guan
Silicon (Si) deficiency and heavy metals (HMs) pollution are common for farmland soil because of long-term intensive farming. In this study, a novel citrate-modified biochar (C-BC) was introduced as a soil conditioner to simultaneously increase the amount of plant-available Si (PASi) and immobilize HMs. The maximum amount of PASi released was 33.00 mg⋅g −1 from C-BC pre-treated with 0.1 mol⋅L −1 citrate (C-BC0.1). A formation–transport coupling mechanism for increasing the amount of PASi released was developed. Stable Si in the biomass was pyrolyzed to give silicate that was relatively mobile via nucleophilic attack of citrate and hydrolysis of amorphous Si. Silicate species were then released through the porous surface and widening cracks caused by pyrolysis . At citrate concentrations >0.1 mol⋅L −1 , the surface and cracks were easily blocked by precipitates formed during pyrolysis. The ability of C-BC to remove HMs was assessed using Cu as an example. C-BC0.1 was optimal for adsorbing Cu, and the maximum adsorption capacity was 271.73 mg⋅g −1 . The Cu adsorption mechanism mainly involved surface precipitation, surface complexation, electrostatic attraction and hydrogen bonding. Our research provides important implications for simultaneously addressing Si deficiency and HMs contaminant problems by these materials for soil amendment in agro-ecosystem.
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