GB629262A - Process for manufacture of magnesium compounds - Google Patents

Abstract

In a process for the manufacture of relatively pure magnesium compounds from brines, e.g. sea water, containing convertible magnesium salts, impure brine is reacted with a lime-containing material to form magnesium hydroxide, which is removed as a slurry from the mother liquor, the slurry being precarbonated to a degree sufficient to convert the dissolved calcium salts to solid phase calcium carbonate and further carbonated to form magnesium bicarbonate in solution, the latter being <PICT:0629262/III/1> removed and converted, e.g. by aeration, to solid magnesium carbonate which is then separated from the effluent. According to Fig. 1, sea water, which may be pre-treated, e.g. by chlorinating and settling out readily-removable solids, is supplied to a precipitating operation 10 wherein brine is reacted with a precipitant such as lime or calcined dolomite from 11 and 12, in the form of a slurry or powder, the resulting precipitate of magnesium hydroxide being allowed to settle in tank 10b, from which dilute slurry is withdrawn and thickened at 13. In order to remove dissolved calcium salts the slurry from 13 is precarbonated at 70 DEG to 90 DEG C. either by passing hot flue gases therethrough or by mixing with bicarbonate solution from line 14. The slurry is then diluted at 16 with effluent 14 and carbonated at 17, insoluble impurities being separated as a sludge at 18 leaving an effluent from which neutral magnesium carbonate is precipitated by aeration at 19 by a neutral gas, e.g. air. After settling at 20 and de-watering and washing at 21, the magnesium carbonate may be further treated to produce other magnesium compounds, e.g. it may be calcined to form magnesium oxide or it may be dried and expanded at 25 to produce basic magnesium carbonate. While a major part of the effluent from the settling operation 20 is shown being returned to the dilution step 16, a minor part is bled off from the system at 22 to maintain the desired salt concentration. Other optional features include: returning a portion of the settled solids from 20 to the aerating step 19 (Specification 580,367), adding a coagulant, e.g. boiled starch, to the precipitant, and using a sintered precipitant (Specification 557,845). Specifications 467,543 and 554,760 also are referred to.