Investigation of microwave roasting for potash extraction from nepheline syenite

A clean method for gallium recovery and the coproduction of silica-potassium compound fertilizer and zeolite F from brown corundum fly ash

Brown corundum fly ash (BCFA) is a solid waste from the brown corundum smelting process that contains abundant Ga, K, Si, and Al, but effectively extracting Ga can be challenging since most of it is located inside the particles. This study proposes a comprehensive utilization method of BCFA that combines hydrothermal leaching and alkali regeneration to extract Ga efficiently while producing silica-potassium compound fertilizer (SPCF) and zeolite F. By utilizing the transformation of phase and structure in the hydrothermal leaching process, Ga extraction is efficiently achieved. The results showed that under the conditions of 210 g/L KOH concentration, a liquidsolid ratio of 25 mL/g, and 160 °C hydrothermal leaching for 60 min, the extraction efficiencies of Ga, K, and Si were 95.91 %, 51.78 %, and 69.57 %, respectively. The solid product's effective SiO2 and K2O contents increased to 24.72 wt% and 17.74 wt%, respectively, which can be further used as SPCF for agricultural production. The hydrothermal leaching solution was regenerated by adjusting the Al/Si molar ratio and crystalizing at 160 °C for 24 h. The Si was recovered in the form of high value-added zeolite F, with only a 3.60 % loss of Ga.

Research on the mechanism of sodium separation in bauxite residue synergy preparation of potassium-containing compound fertilizer raw materials by the hydrothermal method

Bauxite residue poses an increasingly serious ecological safety problem in the alumina industry. A novel process for removing sodium in bauxite residue synergistic preparation of potassium-containing compound fertilizer raw materials was proposed to relieve pressure on the fertilizer industry. In this paper, synthetic sodalite and katoite were used to simulate the main mineral phases of bauxite residue to determine the suitable conditions for the method, and the transformation mechanism of the process was researched by analyzing the phase structure and microscopic morphology of the samples using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and specific surface area detection. The results show that the ideal reaction condition is 320 g/L K₂O with solid reactants at 200 °C for 1 h. The separation rate of Na in the sodalite-katoite mixture reached 93.60%, with potassium aluminum silicate and katoite being the primary phases of the product, with a mesoporous structure and easy to be absorbed by crops. The bauxite residue transformation residue consisted of katoite and kaliophilite. With a total effective K₂O, CaO, and SiO₂ content of 38.22%, the Na₂O content was 0.54%, meeting the requirements of compound fertilizer content on the market. The transformation mechanism is a dissolution-precipitation controlled sodium-potassium ion replacement reaction. This study provides theoretical guidance for the preparation of mineral fertilizer from bauxite residue and has practical production potential, opening up a new perspective for bauxite residue resource usage in the agricultural field.

Nepheline Syenite as an Alternative Source for Aluminum Production

The increasing demand for aluminum in conjunction with the limited available bauxite deposits in Europe results in the dire need for the evaluation of alternative raw materials for the whole value chain of alumina production. The present paper focuses on the possible use of nepheline syenite, originated as a mine byproduct, in alumina production through leaching with an azeotropic HCl solution. Previous work on nepheline syenite dissolution focused more on the extraction of potassium and sodium values. In this work, emphasis is given at the characteristics and leachability of aluminum content phases by applying a high temperature HCl leaching in untreated material. From this point of view, leaching experiments were conducted on nepheline syenite, at a temperature range of 90 °C to 150 °C and with aqueous azeotropic HCl solution. Leaching, in the aforementioned conditions, is a process, characterized by medium aluminum dissolution. The results show that the aluminum-bearing phases that withstand the dissolution process are mainly the ones of sodium and potassium feldspars.

Sustainable Process for the Extraction of Potassium from Feldspar Using Eggshell Powder

To recover potassium from feldspar, a biowaste, i.e., eggshell, was used. The chief composition of eggshells is calcite. As it is a rich source of Ca, hence it is used with HCl to produce calcium chloride. Feldspar is an aluminosilicate mineral that bears potassium in the interstitial sites. To unlock the potassium from the interstitial sites, it was roasted with calcium chloride prepared by mixing eggshell and hydrochloric acid. At the roasting temperature, CaCl₂ melts and penetrates into the aluminosilicate matrix to replace K with Ca. Potassium ion released from the silicate matrix combines with chloride ions to form potassium chloride, which solubilized in water during the leaching process of the roasted feldspar. For elucidation of the mechanism of the roasting process, the shrinking core model was applied to the roast-leach data, and diffusion through the product layer was inferred as the rate-determining step. The order of the roasting process was found to be 2.158 and activation energy calculated to be 155.3 kJ/mol. Apart from potassium, sodium and excess calcium also got co-leached. To recover potassium from the leach liquor selectively, sodium perchlorate was added to precipitate potassium as KClO₄. Further, potassium perchlorate was thermally decomposed to give fertilizer grade potassium chloride (purity: 99.81%).

The Correlation of Roasting Conditions in Selective Potassium Extraction from K-Feldspar Ore

Feldspar minerals are essential ingredients for the glass and ceramic-glass industries. The potassium element found in certain proportions in the composition of K-feldspar minerals has a fundamental function in the growth of plants. The production of potassium fertilizers is mostly made from the soluble minerals, which are located in lakes. Despite having a huge area of use in the agriculture industry, the reserves of these salts are limited and not evenly distributed in the earth’s crust. Due to the high availability of feldspar reserves in the earth’s crust, the production of potential potassium salts can provide a wide range of social and economic benefits. In this study, potassium extraction from a feldspar ore, which contained microcline, albite, muscovite, and quartz, was studied using chloridizing (CaCl2) roasting followed by leaching. Direct leaching experiments were also performed on the sample by adapting various solvents. To emphasize the importance of roasting before the dissolution process, different parameters such as particle size, roasting temperature, and duration, as well as the feldspar/CaCl2 ratio, were tested. Under the optimum conditions (i.e., −106 microns, 850 Co, 60 minutes, 1:1.5 feldspar:CaCl2), 99% of the potassium was successfully extracted from the ore feed.