| Boron slurry is the waste of borax manufacture. The main components of boron slurryare magnesium oxide and silica dioxide. It also contains some iron oxide and alumina oxide,and a small quantity of boron trioxide, calcium oxide and manganese dioxide. Every one tonborax manufacturing brings on four ton boron slurry emission. Boron slurry is not only theoccupation of land, but also produces severity contaminated to environment due to it'salkaline. This makes a negative influence on benefits of the factories. With the evolution ofboron industry and the growing demand of borax and boracic acid in China, the output ofboron slurry has been increased. This makes a large waste of the valuable magnesiumresources. It becomes urgent to be solved that to find a adequate method to recycle thevaluable magnesium resources.Magnesium hydroxide has widespread using as a kind of important inorganic salts.Especially as a kind of inorganic flame retardants, magnesium hydroxide has the advantage ofhigher decomposition temperature, strong smoke inhibition, fine flame-retardant effect andreleasing nonpoisonous and non-corrosive matter. It is highly interested by customers andscientific researchers in recent years. In this article flame-retardant magnesium hydroxide hasbeen prepared from boron slurry by two steps. At first magnesium chloride solution is gottenafter extraction of magnesium under acid leaching and separation of impurities. And then withthe precipitant ammonia water, flame-retardant magnesium hydroxide is synthesized by directprecipitation method.Hydrochloride acid is selected as the leaching agent by comparing the leaching effect ofhydrochloride acid, sulfate acid and ammonia chloride saturated solution through a greatnumber of experiments. The influential factors of magnesium leaching rate is investigated,and the optimal technical process is determined. The first-time magnesium leaching ratereaches to 96.0％and the average magnesium leaching rate is 90.68％. Impurity ions in theleaching solution, such as Fe3+, Al3+ and Mn4+, can be hydrolyzing to precipitate by ammoniadue to their different pH range of hydrolyzing. The synthesis and recycle of the iron-aluminum hydroxide complex has also been discussed preliminarily.Flame-retardant magnesium hydroxide has been prepared from self-made magnesiumchloride solution and ammonia water by direct precipitation method. The influence factors to the settling performance and precipitation rate of magnesium hydroxide, such as feedingmode, reaction temperature, concentration and adding speed of ammonia water, pH value atreaction end, ageing temperature and time and so on, have been discussed by the way ofchemical analysis, X-ray diffraction (XRD), transmission electron microscope (TEM),thermogravimetry analysis, grain size analysis, infrared analysis (IR) and so on. Effect ofdispersant on property of the product is discussed primarily. The optimal technical process isfinally determined. The product is modified by sodium stearate with the concentration of 4％.The grain-size distribution is from 600～1200 nm to 750～850 nm. The purity is around97.8％, which is fit for the need of flame-retardant. XRD analysis indicates product's purity.TG analysis show that the decomposition temperature of product is between 350℃and 450℃, and water loss is 30.1％at 450℃. TEM analysis suggests that the product is needle-likewith the length diameter ratio around 50.
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