Investigation of two-stage depressing by using hydrophilic polymer to improve the process of fluorite flotation

Fluorite is a non-renewable mineral that is used for anhydrous hydrofluoric acid and aluminum fluoride purposes. In China, along with the excellent fluorite resource, which is over-exploited, many off specification fluorites (CaF2 > 93, under 97%; SiO2 > 1.5%) are produced. Improving the grade of fluorite instead of costly technologies of the Buss and CHEMCO are conducted. To improve the grade of fluorite, an excessive amount of sodium silicate is commonly used. However, this approach cannot stably produce high-quality fluorite and result in excessive reagent consumption, poor selectivity and high-water content of the fluorite concentrate. To solve these problems, suitable hydrophilic polymer depressants, which are highly stable, safe, non-toxic, hydrophilic, biodegradable and low processing cost because of abundant in nature, are selected to replace sodium silicate. To make the study practical, the testing location chosen was in Chenzhou (Hunan, China) and was operated by Xinyuan mining Co. Ltd., the largest monolithic fluorite ore producer in Asia. Meanwhile, to prevent the above problems from occurring, the focus throughout this study was achieving separation in the flotation process through the successful occurrence of two sub-processes. The first process was desilicication using dextrin, and the second process was decalcification using tannin. A tech-economic assessment based on the pilot program showed that compared with sodium silicate, the new technology (dextrin + tannin) improved fluorite recovery by 19.23%, removal rate of CaCO3 by 13.43% and SiO2 by 8.93% and reduced production costs by $2914.8 per day. The technology (dextrin + tannin) produced an excellent result, simplifying the flow during fluorite flotation, which can led to a reduction in power consumption as well as reduction in production costs for each ton of 105% sulfuric acid of $3.24 (t/t) for the entire production chain lifecycle. The new technology was an efficient, economic and environmentally friendly and has widespread applications and promising market prospects. (C) 2018 Elsevier Ltd. All rights reserved.