Optimization of operating parameters and rate of uranium bioleaching from a low-grade ore

A comprehensive review of bioleaching optimization by statistical approaches: recycling mechanisms, factors affecting, challenges, and sustainability

A serious environmental problem is associated with the accumulation of solid waste on the Earth. Researchers are encouraged to find an efficient and sustainable method to recover highly profitable heavy metals and precious and base metals. Bioleaching is a green method of recovering valuable metals from solid waste. Optimizing the variables and conditions of the bioleaching process is crucial to achieving maximum metal recovery most cost-effectively. The conventional optimization method (one factor at a time) is well-studied. However, it has some drawbacks, such as the necessity of more experiments, the need to spend more time, and the inability to illuminate the synergistic effect of the variables. Optimization studies are increasingly utilizing response surface methodology (RSM) because it provides details about the interaction effects of variables with fewer experiments. This review discusses the application of RSM for bioleaching experiments from other solid wastes. It discusses the Central Composite and Box-Behnken designs as the most commonly used designs for optimizing bioleaching methods. The most influential factors for increasing the heavy metal recovery rate in applying RSM using the bioleaching process are recognized, and some suggestions are made for future research.

Remediation techniques for uranium removal from polluted environment - Review on methods, mechanism and toxicology

Uranium, a radionuclide, is a predominant element utilized for speciality requirements in industrial applications, as fuels and catalyst. The radioactive properties and chemical toxicity of uranium causes a major threat to the ecosystem. The hazards associated with Uranium pollution includes the cancer in bones, liver, and lungs. The toxicological properties of Uranium are discussed in detail. Although there are many methods to eliminate those hazards, this research work is aimed to describe the application of bioremediation methods. Bioremediation methods involve elimination of the hazards of uranium, by transforming into low oxidation form using natural microbes and plants. This study deeply elucidates the methods as bioleaching, biosorption, bioreduction and phytoremediation. Bioleaching process involves bio-oxidation of tetravalent uranium when it gets in contact with acidophilic metal bacterial complex to obtain leach liquor. In biosorption, chitin/chitosan derived sorbents act as chelators and binds with uranium by electrostatic attraction. Bio reduction employs a bacterial transformation into enzymes which immobilize and reduce uranium. Phytoremediation includes phytoextraction and phytotranslocation of uranium through xylems from soil to roots and shoots of plants. The highest uranium removal and uptake reported using the different methods are listed as follows: bioleaching (100% uranium recovery), biosorption (167 g kg^-1 uranium uptake), bioreduction (98.9% uranium recovery), and phytoremediation (49,639 mg kg^-1 uranium uptake). Among all the techniques mentioned above, bioleaching has been proved to be the most efficient for uranium remediation.

Enhanced effect of biochar on leaching vanadium and copper from stone coal tailings by Thiobacillus ferrooxidans

Among the many extraction technologies for recovering metal resources from tailings, bioleaching technology is gradually showing its momentum. In our research, the enhanced effect of biochar on the bioleaching of stone coal tailings by Thiobacillus ferrooxidans (T. ferrooxidans) has been explored. In the static bioleaching experiment for 10 days, the leaching rate of vanadium (V) and copper (Cu) increased by 26.8% and 21.0% respectively after adding 5 g/L biochar. The dynamic bioleaching experiment further verified that under the promotion of biochar, the 44 day cumulative leaching rate of V and Cu increased by 15.3% and 14.5%, respectively. The promoting effect of biochar on T. ferrooxidans was mainly reflected in two aspects. The unique porous structure of biochar created a microenvironment for free microorganisms for inhabitation, while storing abundant nutrients. Biochar can also act as an excellent electronic medium to promote electron transfer, improving the oxidation ability of T. ferrooxidans on Fe²⁺. Furthermore, the presence of biochar may effectively inhibit the formation of jarosite precipitation on tailings in bioleaching, thereby improving the dissolution of tailings and the release of metal elements. This study demonstrates that biochar-enhanced bioleaching may be an efficient and environmentally friendly method for recovering metal resources from tailings.

Application of response surface method in the separation of radioactive material: a review

Response Surface Method (RSM) is one of the most popular and powerful tools for experimental design and optimization. This paper first reviewed the research progress of RSM in the separation and recovery of various radioactive materials, and verified the application of RSM in adsorption isotherm analysis and thermodynamic calculation. The main advantage of RSM in radioactive material separation is the reduction in the number of experiments required, resulting in considerably less radioactive material consumption, secondary waste generation, workload and radiation dose, which is valuable for the research of radioactive material separation.

Bioleaching Studies of Uranium in a Rock Sample from Sinai Using Some Native Streptomyces and Aspergillus Species

Sinai's important geographical and strategic position is attracting researchers to explore opportunities to maximize exploitation of its treasures, especially in the area of sustainable development. One of the fields of exploitation is extracting valuable metals from low-grade ores using green technologies. In this study, we examined the possibility of microbial leaching of uranium (U) from a rock sample collected from Wadi Naseib, Sinai, Egypt. Twenty previously isolated and tentatively identified native microorganisms, 10 Streptomyces and 10 Aspergillus, were used to make U-bioleaching using cells (direct) and cell metabolites (indirect). The tested isolates showed variable U-bioleaching efficiencies and the highest results was attained via the indirect method (57.2 ± 9.2% and 83.6 ± 2.3%) using two isolates that were identified genotypically as Streptomyces sp. EGY1 and Aspergillus niveus EGY2 respectively. TEM images showed that cells of A. niveus EGY2 made biomineralization, biosorption and bioaccumulation of U. The present study revealed that neither high acid production nor high phosphatase activities guarantees a high U-bioleaching efficiency. Many factors affecting the process were also studied using A. niveus EGY2. The highest U-bioleaching efficiency (87.8 ± 8.7%) was attained using pH 9, 160 rpm of both culturing and bioleaching steps, rock particle size of above 700 µm and 1% pulp density. U was recovered from leach liquor after optimization experiments using NaOH and its concentration was 64.35%. Our study revealed that Aspergillus niveus EGY2 could be promising in future scaling-up studies and pilot trials using the tested rock sample.

Insights into the fluoride-resistant regulation mechanism of Acidithiobacillus ferrooxidans ATCC 23270 based on whole genome microarrays

Acidophilic microorganisms involved in uranium bioleaching are usually suppressed by dissolved fluoride ions, eventually leading to reduced leaching efficiency. However, little is known about the regulation mechanisms of microbial resistance to fluoride. In this study, the resistance of Acidithiobacillus ferrooxidans ATCC 23270 to fluoride was investigated by detecting bacterial growth fluctuations and ferrous or sulfur oxidation. To explore the regulation mechanism, a whole genome microarray was used to profile the genome-wide expression. The fluoride tolerance of A. ferrooxidans cultured in the presence of FeSO4 was better than that cultured with the S(0) substrate. The differentially expressed gene categories closely related to fluoride tolerance included those involved in energy metabolism, cellular processes, protein synthesis, transport, the cell envelope, and binding proteins. This study highlights that the cellular ferrous oxidation ability was enhanced at the lower fluoride concentrations. An overview of the cellular regulation mechanisms of extremophiles to fluoride resistance is discussed.