METHOD FOR PREPARING HIGH-PURITY FLAME-RETARDANT MAGNESIUM HYDROXIDE BY RECOVERY FROM HEAVY-METAL SLUDGE

摘要

Provided is a method for preparing high-purity flame-retardant magnesium hydroxide by recovery from a heavy-metal sludge, comprising the following steps: pretreating and washing with water: adding pure water to the heavy-metal sludge in a mass ratio of the pure water to the dry matter of the sludge of 8 : 1 - 15 : 1, heating same to 80ºC-85ºC and stirring by a stirrer, then adding a dilute sulfuric acid of 0.4 g/L - 0.6 g/L to regulate the pH to 7.0 - 8.0, performing plate-frame pressure filtration dehydration on the resulting mixture of water and slag, to obtain a filtrate 1 and a filter residue 1, washing the filter residue 1 with hot water, filtering and dehydrating 1 - 3 times to obtain a filtrate 2, and combining the filtrate 1 and the filtrate 2, to obtain a filtrate being a magnesium liquid; and successively performing the steps of calcium removal, silicon removal, magnesium deposition by adding an alkali liquid, surface modification, aging, a hydrothermal treatment, dehydration, washing, drying, etc. on the magnesium liquid, to obtain the high-purity flame-retardant magnesium hydroxide. In the method, the purity of the flame-retardant magnesium hydroxide product is further improved while the recovery rates of metal cobalt and nickel are ensured.