Factors affecting bioleaching in the processing of non-metallics

Biotechnological treatment of non-metallics is based on bacterial leaching of raw material and dissolution of Fe. Bacterial iron dissolution ability is dependent on various physicochemical factors as temperature, acidity of solutions, redox potential, rapidity of water circulation and presence of organic sources. The Fe content in the quartz sands and feldspar samples by the biological leaching decreased as much as 60% and by subsequent using of electromagnetic separation of feldspars, the decrease of Fe content in 74% was achieved. However, the application of magnetic separation of quartz sands after bioleaching resulted in total iron removal of 93% and in such combined way prepared product contained 0.024 % of Fe2O3. Achieved results on iron removal point to the fact that combination of leaching and magnetic separation enables to obtain product usable in glass and ceramic industry.

Effects of Various Precipitants on Iron Removal from a Zinc Concentrate Pressure Leaching Solution

Autoclave leaching of zinc concentrate (Sphalerite) is an environmentally friendly process compared to roasting, which discharges pollutants into the atmosphere. Due to the amount of iron in the final product, a study is proposed to evaluate different reagents for eliminating iron from the autoclave outcome, minimizing Zn losses. The colloid formation, zinc losses, iron removal, phase separation stage characteristics (sedimentation and filtering), and reagent costs were used to evaluate six-iron precipitating reagents: CaO, Na2CO3, CaCO3, NaOH, MgO, and Ca(OH)2. CaO shows 99.5% iron removal and 87% zinc recovery. Although CaO was one of the reagents with significant zinc recovery, it presented operational difficulties in the filtration stage due to the high viscosity of the mixtures. Finally, Ca(OH)2 is the reagent recommended due to its ease of use, zinc yield recovery, electrowinning efficiency, and iron precipitate filtration rate. Zinc recovery was above 80%, while the iron concentration in the solution was below 50 ppm.

INTENSIFICATION OF IRON REMOVING OF LOW ALKALINE GROUNDWATER

The problem of providing humanity with quality drinking water is exacerbated in the modern world. According to international organizations, a half of the world's population by 2025 will live in areas with significant water shortages. The sufficient standard of living and environmental safety is one of the citizens’ rights defined by the main law of Ukraine, which provides for the provision of quality drinking water in the required amounts and in accordance with established standards for the quality of drinking water. The Cabinet of Ministers of Ukraine has approved the concept of the state target social program "Drinking Water of Ukraine" for 2022-2026 for this purpose. The unsatisfactory state of water quality in Ukraine is associated with moral and physical depreciation of main resources, underfunding of water supply and sewerage industry. The situation is complicated by the lack of qualified personnel in rural areas. A large part of the inhabitants’ rural settlements use groundwater aquifers for their drinking purposes, which often contain excessive concentrations of total iron. The water treatment facilities were built according to standard designs using non-reagent methods for water iron removal in small settlements. The practice of individual treatment plants operation has shown their low efficiency, due to the unreasonable use of such methods. The improvement of existing water treatment schemes should be carried out taking into account the peculiarities of the physicochemical composition of water and the use of existing water treatment equipment. The purpose of the work is to improve the technological scheme of water iron removal and improve the quality of the filtrate. It is established that the reason for the unsatisfactory operation of treatment plants is due to the low alkalinity of groundwater. The rational types of alkalizing reagents and their calculated doses are substantiated by the results of experimental studies, the dependences of changes in the hydrogen index on the type and dose of reagents, residual alkalinity of water, the efficiency of water iron removal.

Evaluating and Enhancing Iron Removal via Filterable Iron Precipitates Formation during Coal-Waste Bioleaching

Iron removal via jarosite precipitate formation is a commonly used technique in various hydrometallurgical processes. Excess iron removal often becomes essential to an overall metal recovery circuit. This is particularly important to processes involving iron-bearing minerals. A technique, which involved the use of pyrite to generate acid for leaching, for iron removal is critical to enabling the process. Iron removal using CaO or similar reagents is expensive and often results in lost product. In the present study, various compounds that facilitate jarosite formation, namely Na2SO4, NH4OH, KCl, and KOH, were utilized and their effect in precipitation was observed. Visual Minteq assisted simulations were run in order to evaluate favorable conditions for iron removal. Morphology and elemental composition of precipitates were analyzed using scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, and the phase purity was identified using X-ray diffraction analysis.

Strengthened Oxygen Oxidation of Ferrous Ions by A Homemade Venturi Jet Microbubble Generator towards Iron Removal in Hydrometallurgy

Iron normally exists in the form of ferrous ion (Fe2+) in primary ore deposits of valuable metals. To remove iron from hydrometallurgical leaching solution or suspension by precipitation, ferrous ion should be oxidized to ferric ion (Fe3+) first. Due to the low oxidation rate of Fe2+ by the traditional oxygen oxidation method, industry has to use more agitating barrels, steam, and compressed gas, as well as a larger workshop area, which dramatically increases the equipment investment and operation costs. In this study, a strengthened oxygen oxidation method for Fe2+ using a homemade venturi jet microbubble generator is proposed. Microbubbles of air, oxygen, or oxygen-enriched air can be formed in the leaching solution or suspension, which can greatly improve the dissolved oxygen content in the solution and increase the gas-liquid contact area, thereby accelerating the oxygen oxidation rate of Fe2+ to Fe3+ and realizing the rapid iron removal of the leaching solution or suspension. By measuring the residual concentration of Fe2+ in the solution after oxidation reaction, it was found that the pump power, solution temperature, pH, concentration of Cu2+, and solution flow rate had great effects on the oxidation performance of the produced microbubble. By analyzing the images of the microbubbles and measuring the dissolved oxygen content in the solution, it is confirmed that the accelerated oxidation reaction rate of Fe2+ using the new proposed method was mainly due to the increase of the dissolved oxygen amount in the solution. Moreover, this method can significantly increase the purification depth of iron ion, expand production capacity, and decrease energy consumption.

Experimental Study on Biological Treatment of Copper in Acid Mine Drainage after Iron Removal

Acid mine drainage is characterized by low pH value, many types of heavy metals, high concentration of heavy metals and great environmental damage. Copper precipitation by sulfate reducing bacteria is a common method. In this experiment, the AMD after iron removal was treated by an upflow anaerobic bioreactor. The effects of HRT, carbon source type, carbon source dosage and reactor temperature on the operation of the reactor were studied. The optimum process parameters were determined: HRT was 12h, formic acid was used as carbon source and the dosage was 0.5g/L, and the temperature was 30 °C. Under the process conditions, the Cu concentration in the reactor effluent decreased to 0.043mg/L, and the recovery rate of Cu metal was 99.9%. The mechanism of copper deposition in the reactor was studied by characterization of the structure and morphology of the precipitated product and the analysis of the microbial community structure in the effluent of the reactor.