Ruan Chi

Leaching process of rare earths from weathered crust elution-deposited rare earth ore

In order to strengthen the leaching procedure, the chemical processes of leaching rare earths (RE) from the weathered crust elution-deposited rare earth ore were investigated frow the viewpoints of kinetics, hydrodynamic and mass transfer. The results show that the leaching hydrodynamics follows the Darcy law. The leaching kinetics can be described by the shrinking core model; the leaching process is controlled by diffusion of porous solid layer; and the mass transfer can be described with Van Deemter equation. This provides a theoretic basis and a scientific approach with high efficiency and optimized extraction conditions in industrial practice.

Kinetics of thermal decomposition of lanthanum oxalate hydrate

Abstract Lanthanum oxalate hydrate La 2 (C 2 O 4 ) 3 ·10H 2 O, the precursor of La 2 O 3 ultrafine powders, was prepared by impinging stream reactor method with PEG 20000 as surfactant. Thermal decomposition of La 2 (C 2 O 4 ) 3 ·10H 2 O from room temperature to 900 °C was investigated and intermediates and final solid products were characterized by FTIR and DSC-TG. Results show that the thermal decomposition process consists of five consecutive stage reactions. Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods were implemented for the calculation of energy of activation ( E ), and the results show that E depends on α, demonstrating that the decomposition reaction process of the lanthanum oxalate is of a complex kinetic mechanism. The most probable mechanistic function, G (α)=[1−(1+α) 1/3 ] 2 , and the kinetic parameters were obtained by multivariate non-linear regression analysis method. The average E -value that is compatible with the kinetic model is close to value which was obtained by FWO and KAS methods. The fitting curve matches the original TG curve very well.

Evaluation for Rock Phosphate Solubilization in Fermentation and Soil–Plant System Using A Stress-Tolerant Phosphate-Solubilizing Aspergillus niger WHAK1

A strain WHAK1, identified as Aspergillus niger, was isolated from Yichang phosphate mines in Hubei province of China. The fungus developed a phosphate solubilization zone on modified National Botanical Research Institute’s phosphate growth (NBRIP) agar medium, supplemented with tricalcium phosphate. The fungus was applied in a repeated-batch fermentation process in order to test its effect on solubilization of rock phosphate (RP). The results showed that A. niger WHAK1 could effectively solubilize RP in NBRIP liquid medium and released soluble phosphate in the broth, which can be illustrated by the observation of scanning electron microscope, energy-dispersive X-ray microanalysis, and Fourier transform infrared spectroscopy. Acidification of the broth seemed to be the major mechanism for RP solubilization by the fungus. Indeed, multiple organic acids (mainly gluconic acid) were detected in the broth by high-performance liquid chromatography analysis. These organic acids caused a significant drop of pH and an obvious rise of titratable acidity in the broth. The fungus also exhibited high levels of tolerance against temperature, pH, salinity, and desiccation stresses, although a significant decline in the fungal growth and release of soluble phosphate was marked under increasing intensity of stress parameters. Further, the fungus was introduced into the soil supplemented with RP to analyze its effect on plant growth and phosphate uptake of wheat plants. The result revealed that inoculation of A. niger WHAK1 significantly increased the growth and phosphate uptake of wheat plants in the RP-amended soil compared to the control soil.

Effects of Acidiphilium cryptum on biosolubilization of rock phosphate in the presence of Acidithiobacillus ferrooxidans

Abstract The bioleaching of pyrite and biosolubilization of rock phosphate (RP) in 9K basal salts medium were compared by the following strains of an autotrophic acidophilic bacterium, Acidithiobacillus ferrooxidans , a heterotrophic acidophilic bacterium, Acidiphilium cryptum , and mixed culture of At. ferrooxidans and A. cryptum . The results show that A. cryptum is effective in enhancing the bioleaching of pyrite and biosolubilization of RP in the presence of At. ferrooxidans , although it could not oxidize pyrite and solubilize RP by itself. This effect is demonstrated experimentally that A. cryptum enhances a decrease in pH and an increase in redox potential, concentration of total soluble iron and planktonic part bacterial number in the broth during pyrite bioleaching processes by At. ferrooxidans . The mixed culture of At. ferrooxidans and A. cryptum leads to the most extensive soluble phosphate released at 30 °C. Pulp density exceeding 3% is shown to adversely influence the release of soluble phosphate by the consortium of At. ferrooxidans and A. cryptum . It is essential to add pyrite to the 9K basal salts medium for the biosolubilization of RP by the mixed culture of At. ferrooxidans and A. cryptum , and the percentage of soluble phosphate released is the greatest when the mass ratio of RP to pyrite is 1:2 or 1:3.

Solvent extraction of hafnium from thiocyanic acid medium in DIBK−TBP mixed system

Abstract A novel process for the separation of hafnium from thiocyanic acid medium using the mixture of diisobutyl ketone (DIBK) and tributyl phosphate (TBP) as the extractant was developed. This extraction process was investigated experimentally as a function of the amount of TBP added, acidity, zirconium and hafnium concentrations, salting-out agent, temperature, duration, respectively. The results show that hafnium is enriched in the organic layer and zirconium is in aqueous layer in DIBK-TBP system. Under the optimal technological conditions: TBP addition 20% (v/v), aqueous phase acidity 3.0 mol/L, ammonium sulfate addition 0.8–1.25 mol/L, room temperature and extraction time 10 min, the separation factor of hafnium from zirconium is 9.3.

Correlation analysis on partition of rare earth in ion-exchangeable phase from weathered crust ores

Abstract The rare earth(RE) in weathered crust ores mainly exists as ion-exchangeable phase, approximately 80%. The correlation analysis on partition of 376 samples in ion-exchangeable phase from weathered crust ores was conducted. The results show that partition both among heavy RE elements and light RE elements with high partition appears positive correlation, but partition sums between the heavy RE elements and the light RE elements appear close negative correlation obviously. Clear negative correlations exist between the light RE elements (except Ce) and yttrium(Y). Matrix of correlation analysis on this partition can be divided into three zones. The correlated coefficient variation from negative to positive in zones B and C occurs at Gd, so does that in zones B and A (except Ce, Eu, and Sm), suggesting that RE elements can be divided into two groups with Gd as border. This phenomenon is called Gadolinium-broken effect.

Phosphate solubilization in vitro by isolated Aspergillus niger and Aspergillus carbonarius

Two strains of Aspergillus, A. niger and A. carbonarius, were isolated from agricultural soil and a lake, respectively, in China. The two isolates could effectively release soluble phosphate in NBRIP medium containing Ca3(PO4)2 as the sole phosphorus source. Acidification of the broth seemed to be the major mechanism for phosphate solubilization by the isolates, and this had a significant correlation with a drop in pH. High-pressure liquid chromatography analysis indicated the participation of various organic acids, with gluconic acid as the principal component in the process of acidification in the broth. The isolates displayed trends of soluble phosphate release that closely matched the substantial increases in gluconic acid concentration. Abiotic incubation study using organic or inorganic acid to solubilize Ca3(PO4)2 indicated that the content of soluble phosphate released was significantly lower than that of the broth inoculated with the isolates. Higher release of soluble phosphate and pH reduction have occurred when ammonium rather than nitrate served as the sole source of nitrogen with Ca3(PO4)2.

Dephosphorization of High-Phosphorus Iron Ore Using Different Sources of Aspergillus niger Strains

High-phosphorus iron ore is traditionally dephosphorized by chemical process with inorganic acids. However, this process is not recommended nowadays because of its high cost and consequent environmental pollution. With the current tendency for development of a low-cost and eco-friendly process, dephosphorization of high-phosphorus iron ore through microbial process with three different sources of Aspergillus niger strains was studied in this study. Results show that the three strains of A. niger could grow well in the broth, and effectively remove phosphate from high-phosphorus iron ore during the experiments. Meanwhile, the total iron in the broth was also increased. Acidification of the broth seemed to be the major mechanism for the dephosphorization by these strains. High-pressure liquid chromatography analysis indicated that various organic acids were secreted in the broth, which caused a significant drop of the broth pH. Scanning electron microscopy of ore residues revealed that the high-phosphorus iron ore was obviously destroyed by the actions of these strains. Ore residues by energy-dispersive X-ray microanalysis and Fourier transform infrared spectroscopy indicated that the phosphate was obviously removed from the high-phosphorus iron ore. The optimization of the dephosphorization by these strains was also investigated, and the maximum percentages of phosphate removal were recorded at temperature 27–30 °C, initial pH 5.0–6.5, particle size 0.07–0.1xa0mm, and pulp density of 2–3xa0% (w/v), respectively. The fungus A. niger was found to have good potential for the dephosphorization of high-phosphorus iron ore, and this microbial process seems to be economic and effective in the future industrial application.

Kinetics on leaching of potassium from phosphorus–potassium associated ore in HCl–H 3 PO 4 media

Abstract In order to relieve the equipment corrosion, reduce chlorine and increase phosphorus contents in leaching solution, the leaching behavior of potassium from phosphorus–potassium associated ore in the mixed acids of hydrochloric acid and phosphoric acid was investigated. The effects of various factors, such as mass fraction of hydrochloric acid, solid-to-liquid ratio, material ratio (CaF2 dosage (g)/mass of ore (g)) and leaching temperature were comprehensively studied. It was found that the dissolution fraction of potassium can reach more than 86% under the optimum conditions of leaching temperature 95 °C, HCl concentration 10%, leaching time 6 h, solid/liquid ratio 1:5, and material ratio 0.1. In addition, the leaching kinetics of potassium was successfully modeled by a semi-empirical kinetic model based on the classic shrinking core model. The data showed that the leaching process of potassium was controlled by the product layer diffusion and the apparent activation energy for the process was found to be 54.67 kJ/mol over the temperature range from 65 to 95 °C.

Microbial Community Structure of Activated Sludge for Biosolubilization of Two Different Rock Phosphates.

A microbial consortium was directly taken from activated sludge and was used to solubilize rock phosphates (RPs) in a lab-scale bioreactor in this study. Results showed that the microbial consortium could efficiently release soluble phosphorus (P) from the RPs, and during 30-day incubation, it grew well in the bioreactor and reduced the pH of the solutions. The biosolubilization process was also illustrated by the observation of scanning electron microscopy combined with an energy dispersive X-ray spectroscopy (SEM–EDX), which showed an obvious corrosion on the ore surfaces, and most elements were removed from the ore samples. The analysis of microbial community structure by Illumina 16S ribosomal RNA (rRNA) gene and 18S rRNA gene MiSeq sequencing reflected different microbial diversity and richness in the solutions added with different ore samples. A lower richness and diversity of bacteria but a higher richness and diversity of fungi occurred in the solution added with ore sample 1 compared to that of in the solution added with ore sample 2. Alphaproteobacteria and Saccharomycetes were the dominating bacterial and fungal group, respectively, both in the solutions added with ore samples 1 and 2 at the class level. However, their abundances in the solution added with ore sample 1 were obviously lower than that in the solution added with ore sample 2. This study provides new insights into our understanding of the microbial community structure in the biosolubilization of RPs by a microbial consortium directly taken from activated sludge.