| ArticleName |
Neutralization of sulfate solutions in complex treatment of diopsidecontaining processing waste |
| Abstract |
Following respective experimental studies, data were obtained on the qualitative composition of liquid wastes downstream of sulfuric acid treatment of diopside (raffinate). These are 15–25 % solutions of sulfuric acid with the contents of magnesium compounds up to 20 g/l (for pure metal) and aluminum, iron, and titanium contents of up to 20 g/l. A process design solution is proposed for the neutralization of the raffinate after the extraction of scandium compounds, based on the use of magnesium-containing minerals to produce marketable magnesium sulfate heptahydrate (a fertilizer). The possibility of using synthetic brucite (a waste product in the manufacture of refractory materials) as a neutralizing reagent has been established. It has been found that, during the raffinate neutralization, the precipitation rate for iron, aluminum, and titanium hydroxides approaches 100 %. At the same time, a certain part of unreacted magnesium compounds precipitates with the metal hydroxides and may be reused. The resulting solutions are magnesium sulfate brines with the content of magnesium compounds up to 45 g/l for pure metal (and up to 450 g/l for magnesium sulfate heptahydrate). An X-ray phase analysis of the solid product after the vacuum drying of the brines demonstrates that its purity and chemical composition meet the requirements for magnesium-containing mineral fertilizers. The hydroxide precipitate obtained in the process of neutralization was converted to the sulfate form and used as a coagulant to purify model water with the removal of suspended solids (recycled water). The process design solution proposed for the recycling of substandard raffinate may increase the economic efficiency of diopside processing with the output of marketable magnesium sulfate and scandium concentrate. |
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