Papers by Keyword: Leaching

Abstract: This article describes thermodynamic study of hydrometallurgical method for processing of copper arsenious gold-containing raw material. Chemical and phase composition of the material were researched. Calculations of the Gibbs energy change were conducted for possible reactions of the main minerals, present in the raw material, with nitric acid. Eh-pH diagrams and solid/liquid equilibrium distribution diagrams, which were constructed in order to confirm the possibility of obtaining the required reaction products through nitric acid leaching of the studied raw material.

Abstract: The technique of mathematical modeling using the Selector software package has been applied to study the leaching of fluorine from the carbon part of the aluminum electrolysis cell spent lining. Based on the model obtained, the effects of the solvent (caustic soda Na₂O_ку) concentration and the ratio of liquid and solid phases in the pulp on the fluorine extraction have been assessed. The research object was the lining samples by the RUSAL Krasnoyarsk JSC. A thermodynamic assessment of the spent carbon lining components behavior during the alkaline processing has been performed with the introduction of three solvent concentrations into the model: 12.5, 17.5, and 25.0 g/dm³. According to the model solutions, the maximum fluorine extraction (up to 90 %) is achieved when using a reagent with the Na₂O_ку concentrations of 12.5 and 17.5 g/dm³ and a liquid to solid ratio of 8.5÷10:1. Using the model, the phase composition of the cake and the forms, in which fluorine remains in the solid residue (cake), have been determined. Laboratory studies confirm the convergence of the simulation results with the experimental data: solutions have been obtained to crystallize out cryolite (with fluorine and silica content of 50–53 % wt. and 0.11÷0.53 % wt., respectively), which is in demand in the electrolysis of cryolite-alumina melts.

Abstract: Rice husks (RH) are agricultural wastes available abundantly in rice producing country. A by-product obtained from combustion of rice husk is rice husk ash (RHA) which is rich in silica (SiO₂) contents. This paper focused on the effect of acid leaching treatment on rice husk to produce high-purity silica. There are 4 different states of conditions involved; raw rice husk (RRH), treated rice husk (TRH), rice husk ash (RHA), and treated rice husk ash (TRHA). Citric acid; C₆H₈O₇ was used as a leaching agent. TRH and TRHA was leached to see whether treated rice husk before combustion (TRH) or treated rice husk after combustion (TRHA) will produce more high-purity silica. Chemical composition analysis shows high amorphous silica content which is 98.47% with low metallic impurities at 1.0M C₆H₈O₇, 70 oC for treated rice husk (TRH). X-ray diffraction (XRD) pattern shows the presence of amorphous silica in treated rice husk (TRH) and crystalline silica in treated rice husk ash (TRHA). Fragmentation of TRH into small pieces after acid leaching is seen where there is significant increase in the exposed surface areas. High-purity amorphous silica with more than 98% was prepared via citric acid leaching treatment and combustion process.

Abstract: Thiosulphate gold leaching is an alternative technology to the cyanidation of gold ores. Ethylenediaminetetraacetic acid is referred to as EDTA.A study on the leaching kinetics of gold involved in the system S₂O₃^2--EDTA-Cu²⁺ for the gold in this paper. The effect of temperature and of the addition of copper has been also analyzed, temperature has a remarkable effect over the overall reaction rate in the range from 293 to 323k, the result shows that the leaching process conforms to the chemical control model. The concentration of [S₂O₃^2-] considerably affects the leaching rate obtaining a value of for the order of reaction in the range of concentrations from 0.05 to 0.3 mol/L of S₂O₃^2- which obtaining a reaction order of 1.029. Copper addition favored the leaching rate of gold which obtaining a reaction order of 0.441,Thiosulphater addition also favored the leaching rate of gold .kinetics model was established which is 1−(1−x)^1/3=4950.8c (S₂O₃^2-)^1.029c (Cu²⁺)^0.441exp (-9911/8.314T).

Abstract: Six Portuguese magmatic ornamental stones were submitted to Soxhlet experiments during 10,000 hours (approximately 416 days) in order to evaluate how the rain water affects the rock behavior as a dimension stone. Macroscopic alterations were observed in the rock fragments and chemical analysis of leaching water solutions revealed how major elements were mobilized from rock-forming minerals allowing to compare weathering susceptibilities between different natural stones.

Abstract: Rare Earth Element plus Yttrium (REY) is an critical element in green technology and consumer goods. Due to its limited supply, it is necessary to look for alternative sources of REY which one of the potential candidates is coal fly ash. Two samples of coal fly ash which originated from Indonesia were leached in an alkaline solution in order to remove Si and increase REY content. Samples were collected from pulverized coal power plant in East Java (sample T) and West Java (sample I). Leaching conditions were studied including concentration of NaOH, ratio of volume of liquid (L) to weight of solid (S) and leaching time. It was found that the optimum condition was reached at NaOH concentration of 8M, L/S ratio (10 mL: 1 g) and leaching time of 120 min. At this condition, percent removal of Si and REY enrichment were respectively 56.22% and 30% for sample I, and 33.75% and 24% for sample T.

Abstract: Calcium titanate (CaTiO₃) was synthesized through combustion in air from calcium sources of raw minerals (lime-stone and calcite), anatase titanium dioxide (A-TiO₂) and magnesium (Mg). The syntheses were divided into two reactant systems (lime-stone/A-TiO₂/Mg and calcite/A-TiO₂/Mg. Before synthesis, the raw minerals and A-TiO₂ were high-energy milled for 30 min. These powders were then separately mixed with Mg by ball milling. After synthesis, the as-combusted products were leached with 2 M HCl solution to remove by-products and impurities. A sequential mechanism for the in-situ combustion was proposed by using data from simultaneous thermal analysis (STA) together with thermodynamic values calculated with HSC^ software. XRD results showed that the as-leached products from both reactant systems mainly contained CaTiO₃. FT-IR spectroscopy indicated that the as-leached products had Ca-Ti-O and Ti-O functional groups. In addition, SEM observation of the as-leached products revealed cuboid-like crystals with a particle size of about 100 nm.

Abstract: In the article the negative impact of titano-magnetite ore enrichment waste on the environment and the possibility of its use as vanadium-containing raw materials are overviewed. The chemical and mineralogical composition features of various samples of the Kusinsky deposit titanomagnetite ore tails are presented. Different combinations of their roasting processes (with and without salt additives, with oxides, carbonates, or their compositions) and leaching processes (with water or acid) during hydrometallurgical processing were analyzed.The experiment results on the extraction of vanadium in the form of soluble vanadates from the titanomagnetite ore tails by leaching from samples subjected to roasting with soda ash, sodium sulfate, calcium oxide, and sodium chloride in various mass ratios are presented. The significant influence of ore sample chemical composition on the vanadium extraction degree was revealed. It was revealed that for this type of vanadium raw material additives of sodium chloride and sodium carbonate are most preferable from the vanadium extraction degree point of view.

Abstract: To foster a sustainable deployment of the innovative composite material ‘carbon concrete composite’ in the building sector, it is necessary to ensure its resource efficiency and environmental compatibility. The Institute for Building Materials Research of the RWTH Aachen University is therefore investigating the leaching behavior of this material, especially for the case of irrigated façade elements. Laboratory and outdoor exposure tests are run to determine and assess the heavy metal and trace element emissions by leaching. Feasible interconnections between laboratory and outdoor examinations can be used to develop a faster testing of future composite materials. Current results show no critical release of environmental harmful substances from carbon concrete composite.

Abstract: For over 200 years of gold mining, little has been done to minimize the negative impact of gold mine tailings to the environment. The overall generation of tailing by South African gold mining industry is approximately 300 million tons of slimes. This study was conducted to develop an effective chemical treatment process to reduce major heavy metals in the gold mine tailings, to stabilize the treated gold tailings with lime, to enhance its unconfined compressive strength. Two reagents were investigated namely, citric acid and oxalic acid, the concentrations were varied between 0.25 M and 0.5 M. The leaching tests were conducted at temperatures of 25, 50 and 85 °C. The Elemental, mineralogical and micrograph analysis were conducted on the raw gold mine tailing, treated tailings and stabilized tailing. The results showed a higher relative proportion of magnesium, aluminium silicon, iron and sulphate. The relative proportion for all other metals was below 1 wt%. Citric acid proved to be the best chemical reagent and the optimum results were obtained when the leaching tests were conducted at a temperature of 85 °C, with the concentration of 0.5 M. The final treated solid products had major constituents which enhances material strength development, thus silica and aluminium. Stabilising the treated tailings with 30% hydrated lime, improved the unconfined compressive strength from 1.14 MPa to 2.9 MPa.