| The United States, Turkey and Russia are rich in boron ore, and about 90%of boron reserves in the world are in these countries. China ranks the fourth in the boron reserves, mainly distributed in Liaoning, Jilin, Qinghai and Tibet provinces. At present, ore dilution of boron resources in Liaoning and Qinghai provinces are a serious problem due to mining for decades and abandoning low grade ores when mining high grade ores, and the average grade has been less than 10%. As raw materials of boron chemicals, the ore depletion of boron resources will seriously constrain the sustainable development of boron chemical industry. There is a large number of pinnoite ore in Dachaidan area of Qinghai province, these boron resources can not be directly used as raw materials for boron chemicals because of low grade (less than 10%). The purpose of this paper is to enrich pinnoite ore by a flotation method, which can rise the grade of pinnoite ore to meet the requirements of boron chemical industry.At first, pinnoite ore was characterized by chemical analysis, TGA and XRD, the results show that there are two parts in the ore. One part is a useful minerals named as pinnoite (MgO·B2O3·3H2O), and the other is gangues, mainly calcined gypsum, followed by magnesium carbonate, quartz, sodium chloride, clay and so on. Therefore, the aim of this paper is to separate pinnoite from calcined gypsum and other gangues.The effects of type, dosage and combination of flotation assistants, floatation temperature, time, pH value, liquid-to-solid ratio and ultrasonic treatment on the flotation of low grade pinnoite raw ore were investigated, respectively. Based on experiments, suitable processing parameters were obtained, i.e. collectors dodecylamine acetate 1.5 kg/t, sodium oleate 0.15 kg/t, modifier sodium metasilicate 0.92kg/t, liquid-to-solid ratio 6:1, flotation temperature and time,30℃and 10min, pH of ore pulp 9.0～9.2, ultrasonic time 10min. Under these conditions, the B2O3 content in pinnoite concentrate was increased by 4-6%through reverse flotation. In addition, the impact of scrubbing on the flotation was also investigated, and the results show that scrubbing can remove the soluble salt from raw ore, and greatly improve the reverse flotation of pinnoite raw ore. The XRD characterization and chemical analysis of boron concentrates and tailings showed that pinnoite and calcined gypsum has been basically separated through reverse flotation.The ores was characterized by infrared spectroscopy (IR), ZETA potential and Scanning Electron Microscopy (SEM) to get an insight into the adsorption of ore surfaces, the electrokinetic of ores and the behavior of the solution chemistry. The primary mechanism of interactions between floatation agents and minerals and the process behavior of flotation were discussed in the flotation process. H(Ol)2-and Ol- of anionic collector sodium oleate in solution played important roles and was attached to the surface of pinnoite, so pinnoite became more hydrophilic. Cationic collector dodecylamine acetate was adsorbed to the surface of the calcined gypsum mainly due to the electrostatic attraction between RNH2·RNH3+(a little of RNH3+and (RNH3+)22+) in DAA solution and [SO4]2-with negative charge in the structure of calcined gypsum. In addition, DAA has very strong foamability which is helpful for froth flotation. The hydrophilic and negatively charged silica particles (or colloidal silica) and SiO(OH)3-in sodium metasilicate solution play very important roles in flotation and such strongly hydrophilic particles attached to the surface of pinnoite can depress the flotability of pinnoite. Meanwhile, clay can also be dispersed by sodium metasilicate.
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