Study on preparation of magnesium hydroxide from calcium magnesium nitrate leaching pretreatment of phosphate rock with high content of magnesium and calcium
The decomposition of calcium magnesium carbonate salts by calcining phosphate rock with high content of mag-nesium and calcium can effectively improve the grade of phosphate rock.Leachate and phosphate rock with low magnesium content are obtained by further hydrating and leaching the calcined phosphate rock.The leachate is further precipitated to prepare magnesium hydroxide.However,there are difficulties in solid-liquid separation and low product purity in the produc-tion process of magnesium hydroxide.The properties,specific resistance,and settling performance of wet filter cakes pre-pared at different temperatures were systematically studied.The results showed that the filter cakes adsorbed more water at lower temperatures,making filtration difficult and washing burdensome.When the temperature was rised to 70℃,the mag-nesium hydroxide colloid could be effectively destroyed,thus reducing the adsorption of water by filter cake,reducing the washing burden,and significantly improving the settlement and filtration performance of magnesium hydroxide.The sedi-mentation rate was up to 0.051 8 mL/min,and the minimum specific resistance of filtration was(5.82±1.1)×1011 m/kg.The recovery ratio of magnesium could reach 72%.Further simulation analysis of the precipitation process showed that the two-step precipitation method could realize the pre-separation of impurities,thus improving the purity of magnesium hydroxide,and the product purity could meet the requirements of industrial magnesium hydroxide grade Ⅲ.
magnesium hydroxidespecific resistance of filtrationsettlement performanceVisual MINTEQ simulation
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