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Ciprofloxacin (CIP), a compound with bioaccumulation toxicity and antibiotic resistance, is frequently detected in water at alarming concentrations, which is becoming an increasing concern. In this study, a low-cost ceramsite was developed from industrial solid wastes through sintering to remove CIP from wastewater. The effects of adsorbent dosage, initial pH, contact time, initial CIP concentration, and temperature were explored. More than 99% of CIP (20–60 mg/L) was removed at around pH 2–4 by the ceramsite. The kinetic data fitted well with the pseudo-second-order model, revealing that chemisorption was the main rate-determining step. The isotherm data was better described by the Freundlich model, suggesting that CIP was removed by the formation of multiple layers on the heterogeneous surface. Moreover, the removal efficiency was practically higher than 95% during five regeneration cycles, when different regeneration methods were used, including calcination, HCl, and NaOH washing, indicating that the ceramsite exhibited outstanding reusability in removing CIP. The primary mechanism of CIP removal by the ceramsite was found to be the synergism of adsorption and flocculation, both of which depended on the release of Ca2+ from the ceramsite. In addition, strong Ca-CIP complexes could be formed through surface complexation and metal cation bridging between Ca2+ and different functional groups in CIP.

A passive treatment process using sulfate-reducing bacteria (SRB) is known to be effective in removing heavy metals from acid mine drainage (AMD), though there has been little discussion of the mechanism involved to date. In this work, a sulfate-reducing column test was carried out using supplementary ethanol as an electron donor for microorganisms, and the reaction mechanism was examined using geochemical modeling and X-ray absorption fine structure (XAFS) analysis. The results showed that Cu was readily removed from the AMD on the top surface of the column (0–0.2 m), while Zn and Cd depletion was initiated in the middle of the column (0.2–0.4 m), where sulfide formation by SRB became noticeable. Calculations by a developed geochemical model suggested that ethanol decomposition by aerobic microbes contributed to the reduction of Cu, while sulfide produced by SRB was the major cause of Zn and Cd removal. XAFS analysis of column residue detected ZnS, ZnSO4 (ZnS oxidized by atmospheric exposure during the drying process), and CuCO3, thus confirming the validity of the developed geochemical model. Based on these results, the application of the constructed geochemical model to AMD treatment with SRB could be a useful approach in predicting the behavior of heavy metal removal.

Bioleaching of arsenic (As)-rich, so-called “dirty” concentrates can produce additional Cu value from the flotation waste while simultaneously releasing toxic As. This study bioleached three such concentrates of varying pyrite/enargite ratios ([Py]/[Ena] = 0.7, 1.3 and 2.4) at a pulp density of 20%. The dissolution behavior of Cu and As in relation to the solution redox potential (Eh) was studied with and without activated carbon (AC) as a potential Eh-controlling catalyst. At this high pulp density, Eh was naturally suppressed, without a need for AC dosing, to

Chile and Indonesia, as a mining-developed country and a mining-developing country, respectively, are compared to estimate the future applicability of bioleaching technique into real operation. Chilean copper industry has improved via the following steps: (i) domination by foreign capitals, (ii) resource nationalization, (Chilenization), (iii) lost competitiveness due to the decrease in the ore-grade, (iv) the invitation of foreign capitals to regain the competitiveness. Indonesia takes the same path and it was easily predicted that Indonesian copper mining industry is also likely to loose the competitiveness due to the decrease in ore-grade. Therefore, the installation of bioleaching would be proposed for further development of Indonesian copper industry.

Cadmium (Cd), as a type of heavy metal, can increase the incidence of many diseases, even in low concentrations. In this study, tobermorite was hydrothermally synthesized and then applied to adsorb Cd2+ from an aqueous solution. The physicochemical characteristics of the synthesized tobermorite were detected, and the results indicated that the well-crystallized tobermorite had a lot of mesopores and a large specific surface area of 140.92 m2/g. It acquired a pH self-adjustment ability via spontaneously releasing Ca2+ and OH- into the aqueous solution. The effects of different factors on Cd2+ removal were investigated. For Cd2+, the removal efficiency could reach 99.71% and the maximum adsorption capacity was 39.18 mg/g using tobermorite. The adsorption data was best fitted with the pseudo-second-order kinetic and Langmuir isotherm models. In addition, there was no strict limit on the solution pH in Cd2+ adsorption because the tobermorite could adjust the solution pH to an alkaline atmosphere spontaneously. The efficient removal of Cd2+ using tobermorite was a result of surface complexation and ion exchange.

Overcoming the slow-leaching kinetics of refractory primary copper sulfides is crucial to secure future copper sources. Here, the effect of carbon was investigated as a catalyst for a bioleaching reaction. First, the mechanism of carbon-assisted bioleaching was elucidated using the model chalcopyrite mineral, under specified low-redox potentials, by considering the concept of Enormal. The carbon catalyst effectively controlled the Eh level in bioleaching liquors, which would otherwise exceed its optimal range (0 ≤ Enormal ≤ 1) due to active regeneration of Fe3+ by microbes. Additionally, Enormal of ~0.3 was shown to maximize the carbon-assisted bioleaching of the model chalcopyrite mineral. Secondly, carbon-assisted bioleaching was tested for three types of chalcopyrite/enargite-bearing complex concentrates. A trend was found that the optimal Eh level for a maximum Cu solubilization increases in response to the decreasing chalcopyrite/enargite ratio in the concentrate: When chalcopyrite dominates over enargite, the optimal Eh was found to satisfy 0 ≤ Enormal ≤ 1. As enargite becomes more abundant than chalcopyrite, the optimal Eh for the greatest Cu dissolution was shifted to higher values. Overall, modifying the Eh level by adjusting AC doses to maximize Cu solubilization from the concentrate of complex mineralogy was shown to be useful.

Bioleaching of arsenic (As)-rich, so-called “dirty” concentrates can produce additional Cu value from the flotation waste while simultaneously releasing toxic As. This study bioleached three such concentrates of varying pyrite/enargite ratios ([Py]/[Ena] = 0.7, 1.3 and 2.4) at a pulp density of 20%. The dissolution behavior of Cu and As in relation to the solution redox potential (Eh) was studied with and without activated carbon (AC) as a potential Eh-controlling catalyst. At this high pulp density, Eh was naturally suppressed, without a need for AC dosing, to

Effect of silver (Ag) catalyst in bioleaching of enargite (Cu_3AsS_4) concentrate was studied using mixed cultures of moderately thermophilic acidophilic microorganisms at 45ºC. Addition of Ag_2S enabled selective Cu dissolution from enargite while suppressing pyrite oxidation: At the highest Ag_2S concentration of 0.04%, Cu recovery reached 96% while Fe dissolution was suppressed to reach only 29% by day 72. Overall results from thermodynamic calculation, liquid/solid analyses and kinetic study suggested that Ag-catalyzed bioleaching of enargite concentrate proceeds via formation of at least two types of secondary products (chalcocite, Cu_2S; trisilver arsenic sulfide, Ag_3AsS_4): Addition of Ag_2S as Ag catalyst thermodynamically and microbiologically contributed to lowering solution redox potentials during bioleaching, consequently satisfying Eox (Cu_2S) < E_h < E_c (Ag+) to enhance enargite dissolution via formation of chalcocite intermediate. Formation of trisilver arsenic sulfide and its intermediate layer (Cu,Ag)_3AsS_4 indicated that Cu ion in the enargite lattice is gradually substituted with Ag. Such secondary products did not impose a rate-limiting step, since the Ag-catalyzed bioleaching was shown to be controlled by a chemical surface reaction, rather than diffusion through product film which was the case in the absence of Ag_2S.