Calcium nitrate generating out of nitrogen-acid solutions after breaking up slurries of titanium production

Abstract

This article provides the results of studies of qualitative, quantitative and material composition of titanium production slurry, which is man-made waste. The leaching of slurry parameters by nitric acid are studied: concentration, solid to liquid ratio, temperature and time. The effective leaching parameters were determined: 1.7 mol/l of nitric acid concentration, solid to liquid ratio = 1:8, pH<1, temperature 20±5 ºС, leaching time is 30 minutes. The rate of filtration was 0.035-0.044 m3/ m2×h. A gradual leaching method was used to improve the solutions filtration. At the beginning, the slurry was leached with a 0.5 mol/l HNO3 solution at room temperature for 10 min at solid to liquid ratio = 1:10, the filtration rate was 0.062 m3/ m2×h. Then the cake was again leached with 3.5 mol / l HNO3 at room temperature for 30 min at solid to liquid ratio = 1:10, the filtration rate was 0.094 m3/ m2×h. Calcium hydroxide or lime milk was selected as the reagent to precipitate impurities out of solutions. The content of impurities of iron, titanium and aluminum is significantly reduced when 2.8-5 pH values. The best purification of calcium nitrate solutions by lime milk was at pH 8. Calcium nitrate crystals were obtained by evaporation of a purified solution of 8 pH value out of a slurry leaching when 5% ammonium nitrate was added to it by weight of Ca(NO3)2. The dehydrated calcium nitrate was obtained by granulating 92-95% of the melt in the form of flakes at 90 °C of a surface temperature of the granulator plate.