Mekhanobr Engineering JSC (Russia):

Asonchik K. M., Ph. D. in Engineering Sciences, Leading Researcher, science@mekhanobr.spb.ru

Kostrov А. М., Chief Project Engineer

TVEL Ltd (Russia):
Utin A. V., Deputy General Director
Kovkova T. M., Senior Researcher

Ore mass, delivered to the Lomonosovsky MCC concentrating plant, contains 50–80 % of clay mineral saponite. When interacting with water, clay swells, forming fine-dispersed jelly-like suspension with particle size below 5 microns, practically not precipitating from solution. The paper describes the pilot-scale testing tailings slurry carbonization process, demonstrating a high-efficiency settling of solid particles. Carbonization is a chemicophysical process of pure carbon-dioxide gas interaction with water, contained in tailings slurry. With CO₂ solution carbonic acid is formed, which, interacting with calcium and magnesium ions, contained in saponite, forms water-soluble hydrocarbonates. With that, concentration of Ca²⁺ and Mg²⁺ ions in solution is increased from 3.2–3.8 to 47–134 mg/l, that of hydrocarbonates — from 229 to 1430 mg/l. Separation of calcium and magnesium ions into solution breaks colloidal structure of saponite, resulting in separation of plain water. A pilot-plant equipment – saturator with capacity of 1 m³/hr was developed and designed for performance of carbonization process studies. Settling of carbonized slurry with solids concentration of 94 g/l was estimated by the volume of clarified water in one liter cylinders. The volume of clarified layer of water after 24-hour settling amounted to 30 % of the initial volume, and subsequently increased to 40 % after 5-day settling. Solids concentration in precipitate increased from 94 to 152 g/l. With that, the volume of clarified layer of water after 5-day settling of untreated (non-carbonized) slurry amounted only to 8 %. Carbonization process was monitored with addition of a limited volume (15 m³) of carbonized slurry (consumption of CO₂ – 70 g/m³) into a 300 m³ vessel, filled with untreated slurry with solids concentration of 110 g/l. After 2-day settling, the height of layer of clarified water in vessel with depth of 900 mm amounted to 290 mm, with solids concentration in precipitate – 158 g/l. As a result of solid particles settling with subsequent consolidation of 1 ton of sediment, at least 3 m³ of water were separated, with sludge particles concentration below 0.5 g/l, suitable for utilization in the concentrating plant return water system. Introduction of the described technology following performance of full-scale testing may solve the problem of the Lomonosovsky MCC return water system.

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