Acid leaching of magnesium from saponite clay

This study investigates the acid leaching process for the extraction of magnesium from saponite clay, a by-product of diamond enrichment at the Lomonosov deposit. Saponite, a member of the smectite (montmorillonite) group, is a clay mineral known for its natural filtration and ion exchange properties. Its chemical composition is generally expressed as (Ca, Na)03(Mg, Fe)3(Si, Al)4O10(OH)2·4H2O. The crystals represent aluminum-oxygen layers interleaved with siliconoxygen layers in an octahedral arrangement. Saponite is identified as a magnesian analogue of smectite, containing approximately 33 % by weight of magnesium in terms of its oxide. In the structure of saponite, magnesium occupies the interlayer space as an exchangeable cation. The acid leaching process for magnesium extraction from saponite involves sequential treatment of the ore with hydrochloric acid at varying concentrations. In the initial phase, 15 % hydrochloric acid was applied to the saponite clay at 110 °C, with stirring at 300 rpm for 25 minutes. The resulting suspension was then separated by filtration. Subsequently, 40 ml of ammonia (1 : 1) was added to the filtrate, stirred at 300 rpm for 20 minutes, and again separated by filtration. In the final stage, 0.1 M Na2HPO4 was added to the filtrate in a 1 : 2 ratio at 100 °C, with stirring at 300 rpm for 20 minutes, after which the suspension was filtered once more. Following the completionof the acid leaching process, a basic flowchart outlining the method for producing magnesium phosphate was developed. The overall yield of the target product, accounting for losses during the process, was found to be 82 %.