METHOD OF REWORKING SLUDGE OF CHROMATE PROCESS Russian patent published in 2006 - IPC C01G37/14 

FIELD: method of reworking sludge in production of chromium compounds obtained through oxidizing decomposition of ores found in ponds presenting ecological danger.

SUBSTANCE: proposed method includes treatment of suspension with carbon dioxide, separation of solid residue, decarbonization of magnesium bicarbonate, separation of basic magnesium carbonate residual, drying and calcination. Prior to carbonization of sludge, it is treated with mother solutions obtained after separation of basic magnesium carbonate. Preliminary treatment of sludge with mother solution is performed at intensive mixing continued for 10-30 min at temperature of 30-90°C. After preliminary treatment, sludge suspension is subjected to filtration or settling for obtaining sodium chromate solution cleaned of magnesium; this solution is directed to main process of sodium production or for extraction of chromium oxide. Carbonization is performed by counter-flow scheme at several stages at solid-to-liquid ratio of 12-20; duration of each stage is 30-120 min. Decarbonization of magnesium bicarbonate solutions is performed at temperature of 40-60°C and pH of 7.0-7.3 at mixing.

EFFECT: enhanced efficiency of waste-free technology.

5 cl, 3 tbl, 26 ex