Preparation method for magnesium hydroxide

Abstract

The invention discloses a preparation method for magnesium hydroxide. The method comprises the following steps (1) adding calcined quicklime into a digestion medium solution and carrying out a digestion reaction at a temperature of 30 to 95 DEG C so as to obtain lime milk, wherein anion in the digestion medium solution comprises one or more selected from the group consisting of Cl-, Br-, I- and NO3-; and (2) adding the prepared lime milk into a bischofite solution, carrying out a reaction at a temperature of 20 to 80 DEG C and then carrying out solid-liquid separation so as to obtain a primary magnesium hydroxide solid and a primary filtrate. The preparation method for magnesium hydroxide provided by the invention overcomes the problem that a magnesium hydroxide product prepared from lime is too low and successfully realizes preparation of a high purity magnesium hydroxide product by using a low-cost process; through regulation and control of the structure of slaked lime, the pH value of the lime milk is decreased, a precipitation reaction rate is slowed down, the crystal nucleus of magnesium hydroxide can fully grow before aggregation with other crystal nucleuses, and the probability of entrainment of impurities in reaction products is reduced.

Description

technical field [0001] The invention belongs to the field of salt lake chemistry, and in particular relates to a method for preparing high-purity magnesium hydroxide by a lime method. Background technique [0002] Magnesium hydroxide is the main magnesium compound product in the deep processing of magnesium resources, and its main uses are wastewater treatment, flue gas desulfurization, and flame retardant for engineering materials. At present, the preparation of magnesium hydroxide mainly has the following two ways: one is to use natural brucite resources to produce magnesium hydroxide through refining; the other is to prepare magnesium hydroxide by chemical synthesis from raw materials containing magnesium, and the commonly used raw materials containing magnesium There are bitter soil, sea water, brine and so on. [0003] my country is a country rich in magnesium resources. Only the reserves of magnesium salts in salt lake brine in Qinghai Qaidam Basin reach 4.81 billion ...

AI Technical Summary

Problems solved by technology

In addition, traditional lime digestion generally uses water as the digestion medium. The pH of the digested product - lime milk is relatively high (generally 12.3-12.8 at 25°C), and the reaction speed with magnesium-containing solutions is relatively fast. Magnesium hydroxide crystal nuclei After the formation, it is too late to grow completely and aggregate with other crystal nuclei. During the aggregation process, a certain amount of unreacted CaO and other impurities will inevitably be entrained into the magnesium hydroxide product, making it difficult to obtain high-purity magnesium hydroxide products.

Patent document US4472370 discloses a method for preparing milk of lime, the technical effect of which is focused on increasing the specific surface area and particle size of magnesium hydroxide crystals, although the method of this application can be used to prepare calcium hydroxide prepared by more conventional methods Milk of lime with weakened alkalinity, but when it is applied to the preparation of magnesium hydroxide, it still faces the problem that the purity of magnesium hydroxide needs to be improved