Impact of calcium and gypsum on separation of scheelite from fluorite using sodium silicate as depressant

Solventing out crystallization-basic magnesium carbonate percipitation for thorough phosphorus removal from ammonium tungstate solution

The ammonium tungstate solution obtained by leaching scheelite with phosphate contains a large amount of phosphorus. For production of qualified ammonium paratungstate products, phosphorus must be deeply removed from the ammonium tungstate solution. In this study, a novel process for ammonium phosphate recovery and deep phosphorus removal from the solution was proposed. First, ammonium phosphate was crystallized and separated from the ammonium tungstate solution by blowing ammonia and cooling. Results showed that the crystallization ratio of phosphorus was above 95% under the conditions of an ammonia concentration of 4.18 mol/L, an initial phosphorus concentration ranging from 15 g/L to 30 g/L, a holding time of 60 min and the temperature of 20°C. Then, the small portion of phosphorus remaining in the ammonium tungstate solution was further deeply removed by basic magnesium carbonate percipitation. The phosphorus removal efficiency was above 99% and tungsten loss was less than 0.22% under the following conditions: the basic magnesium carbonate stoichiometric ratio was 1.5, the initial phosphorus concentration was ranging from 0.5 to 4 g/L, the reaction time was 120 min and temperature was 25°C. After phosphorus removal, the concentration of phosphorus in the ammonium tungstate solution was below 10 ppm, which meant deep phosphorus removal was achieved.

Selective Separation of Fluorite from Scheelite Using N-Decanoylsarcosine Sodium as a Novel Collector

Fluorite and scheelite, which are strategic calcium-bearing minerals, have similar active sites (Ca2+); as a result, the efficient separation of the two minerals is still one of the world’s most difficult problems in the field of flotation. In this work, N-decanoylsarcosine sodium (SDAA), a non-toxic and low-cost amino acid surfactant, was applied in the flotation separation of fluorite from scheelite for the first time. In the test, single mineral, binary mixed minerals, and actual ore experiments showed that the pre-removal of fluorite from scheelite by reverse flotation can be achieved. The results of adsorption capacity detections, zeta potential tests, and FTIR analysis showed that the negatively charged SDAA prefers to adsorb onto the positively charged fluorite surface due to the electrostatic interaction. The results of crystal chemistry and DFT calculations showed that SDAA has a stronger chemical interaction and more electron transfer numbers to the Ca atom on the fluorite surface and forms a Ca-SDAA complex. Therefore, the significant difference in the adsorption behavior of SDAA on the surfaces of two minerals provided a new insight into the separation efficiency of amino acids and possesses a great potential for industrial application in scheelite flotation.