The detoxification potential of ferric ions for bioleaching of the chalcopyrite associated with fluoride-bearing gangue mineral

The role of plant growth promoting rhizobacteria in strengthening plant resistance to fluoride toxicity: a review

A wide variety of bacteria are present in soil but in rhizospheric area, the majority of microbes helps plant in defending diseases and facilitate nutrient uptake. These microorganisms are supported by plants and they are known as plant growth-promoting rhizobacteria (PGPR). The PGPRs have the potential to replace chemical fertilizers in a way that is more advantageous for the environment. Fluoride (F) is one of the highly escalating, naturally present contaminants that can be hazardous for PGPRs because of its antibacterial capacity. The interactions of F with different bacterial species in groundwater systems are still not well understood. However, the interaction of PGPR with plants in the rhizosphere region reduces the detrimental effects of pollutants and increases plants' ability to endure abiotic stress. Many studies reveal that PGPRs have developed F defense mechanisms, which include efflux pumps, Intracellular sequestration, enzyme modifications, enhanced DNA repair mechanism, detoxification enzymes, ion transporter/antiporters, F riboswitches, and genetic mutations. These resistance characteristics are frequently discovered by isolating PGPRs from high F-contaminated areas or by exposing cells to fluoride in laboratory conditions. Numerous studies have identified F-resistant microorganisms that possess additional F transporters and duplicates of the well-known targets of F. Plants are prone to F accumulation despite the soil's low F content, which may negatively affect their growth and development. PGPRs can be used as efficient F bioremediators for the soil environment. Environmental biotechnology focuses on creating genetically modified rhizobacteria that can degrade F contaminants over time. The present review focuses on a thorough systemic analysis of contemporary biotechnological techniques, such as gene editing and manipulation methods, for improving plant-microbe interactions for F remediation and suggests the importance of PGPRs in improving soil health and reducing the detrimental effects of F toxicity. The most recent developments in the realm of microbial assistance in the treatment of F-contaminated environments are also highlighted.

Purification and water resource circulation utilization of Cd-containing wastewater during microbial remediation of Cd-polluted soil

The purification and water resource circulation utilization of cadmium-containing leachate is a key link in the field application of microbial remediation in Cd-polluted soil. In this study, through a simulation experiment of microbial remediation of Cd-polluted paddy soil, the feasibility of the purification and recycling process of wastewater derived from microbial remediation of Cd-polluted soil was explored. The results of the microbial mobilization and removal experiment showed that the concentrations of Cd, N, P, and K in the leachate were 88.51 μg/L, 38.06, 0.53, and 98.87 mg/L, respectively. The leachate also contained a large number of microbial resources, indicating that it had high recovery values. To recycle this wastewater, activated carbon (C), humic acid (H), and self-assembled monolayers on mesoporous supports (SAMMS; S) were used as adsorbents. The results showed that the co-existing cations in the leachate had a major influence on the adsorption of Cd. In the ternary system of Fe, Al, and Cd, the removal efficiency of Cd increased to 91.2% when the S dosage was increased to 5‰, and the sorption of Cd occurred after Fe and Al. However, C and H exhibited poor adsorption performances. The isotherm models further showed that the maximum adsorption capacities of S, H, and C were 13.96, 6.41 and 2.94 mg/g, respectively. The adsorption kinetics of S showed that adsorption was a rapid process, and the C-H and O-Si-O of S were the key functional groups. The pH of the leachate significantly affected the adsorption efficiency of Cd. Finally, the purified leachate was successfully applied to microbial cultivation and soil remediation. Overall, the reclamation of Cd-containing wastewater can not only dampen the impacts of water shortages, but also achieve the purposes of Cd removal and resource recovery to lower costs by approximately 1166-3499 yuan per mu.

Mechanical Activation on Bioleaching of Chalcopyrite: A New Insight

Mechanical activation as a means of accelerating the mineral dissolution may play an important role in chalcopyrite bioleaching. In the present work, the mechanical activation by ball-milling with 10 min, 30 min, 60 min, 90 min, 120 min and 180 min time periods of bioleaching of chalcopyrite was studied, and then evaluated by a Density Functional Theory (DFT) calculation. The results showed that the specific surface area increased sharply in the very beginning of mechanical activation and then increased slowly until the agglomeration of the particles occurred, while the chalcopyrite lattices increased with the mechanical activation. The reaction activity analyzed by cyclic voltammetry (CV) increased slowly in 30 min, increased quickly in the following 90 min, and then decreased, while the hydrophobicity analyzed by contact angles of the chalcopyrite after activation showed less of a change. The results showed that after 15 days of bioleaching, the Cu leaching by Sulfobacillus thermosulfidooxidans (S. thermosulfidooxidans) increased from 9.39% in the 0 min of mechanical activation to 87.41% in the 120 min of mechanical activation, and the copper leaching rate increased by about 78%. The DFT results provide solid proof that the activated chalcopyrite can be adsorbed more easily by cells with higher adsorption energies and stronger bonds.

Optimization of the Heap Leaching Process through Changes in Modes of Operation and Discrete Event Simulation

The importance of mine planning is often underestimated. Nonetheless, it is essential in achieving high performance by identifying the potential value of mineral resources and providing an optimal, practical, and realistic strategy for extraction, which considers the greatest quantity of options, materials, and scenarios. Conventional mine planning is based on a mostly deterministic approach, ignoring part of the uncertainty presented in the input data, such as the mineralogical composition of the feed. This work develops a methodology to optimize the mineral recovery of the heap leaching phase by addressing the mineralogical variation of the feed, by alternating the mode of operation depending on the type of ore in the feed. The operational changes considered in the analysis include the leaching of oxide ores by adding only sulfuric acid (H2SO4) as reagent and adding chloride in the case of sulfide ores (secondary sulfides). The incorporation of uncertainty allows the creation of models that maximize the productivity, while confronting the geological uncertainty, as the extraction program progresses. The model seeks to increase the expected recovery from leaching, considering a set of equiprobable geological scenarios. The modeling and simulation of this productive phase is developed through a discrete event simulation (DES) framework. The results of the simulation indicate the potential to address the dynamics of feed variation through the implementation of alternating modes of operation.