Boron mud was solid waste produced by boron chemical industry. Due to the low grade sedimentary metamorphic boron deposits in Northeast China. A large amount of alkaline slag was produced in the production of borax, which directly polluted the environment. About 40% of magnesium oxide was contained in boron mud. Acid leaching method was used to recover magnesium from boron mud. However, the boron mud was directly acid-leached to extract magnesium oxide, and a large amount of sulfuric acid was consumed in the acid-leaching process. Because there was a large amount of MgCO3 in the boron mud, the reaction was violent at the beginning of the experiment, and a large amount of CO2 was generated, which made the leachate easy to overflowed. Therefore, the boron mud was pretreated to promote the leaching of MgO and reduce the amount of sulfuric acid in the experiment. Explore the effect of activation pretreatment of boron mud on the leaching of MgO from it. Boron mud contains MgCO3 and Mg2SiO4. After high temperature activation, MgCO3 released CO2 and turned into MgO, which could not only improve the reactivity, but also reduce the risk of the leachate overflow in the test. Different concentrations of sulfuric acid solution were prepared according to the set conditions, and the boron mud was activated at the set activation temperature. Grinding and magnetic separation of the two kinds of boron mud to reduce the influence of impurity element iron on the purity of crystals. Activated and unactivated boron mud were selected as raw materials. The effects of acid leaching temperature (T), acid leaching time (t), sulfuric acid concentration (ω) and liquid-solid ratio (L/S) on the leaching rate of MgO from boron mud were studied. Under the same experimental conditions, the change of magnesium oxide leaching rate between activated boron mud and unactivated boron mud was studied in this experiment. The primary and secondary factors affecting the leaching rate of magnesium oxide from boron mud were determined by orthogonal test. The concentration of magnesium ions in the solution was determined by ethylenediamine tetraacetic acid (EDTA). Chemical and phase compositions as well as micro-structures of the raw materials, crystalline product, acid leaching residue were analyzed and characterized by chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that boron mud was activated could change its morphology and phase composition, and the leaching rate of magnesium oxide was improved. The main factor affecting the leaching of MgO was ω and T, t and L/S were secondary factors. The product obtained by low-temperature cooling and crystallization was feed grade magnesium sulfate heptahydrate which meets the national standards. The main component of the acid leaching residue was amorphous silica, which could be used to prepare white carbon black. When the experimental factors such as T, t, ω and L/S were low, the leaching rate of MgO was higher than that of unactivated boron mud. However, when the experimental factors were high, the leaching rate of MgO similarly. Due to the high content of MgO in activated boron mud, the leaching amount of MgO was still higher than that of unactivated boron mud under the same conditions. When the two leaching rates were the same, the reduction in the amount of sulfuric acid in the experiment was also very obvious. The best process conditions for acid leaching activated boron mud were cid leaching temperature of 100 ℃, time of 2.5 h, sulfuric acid concentration of 60%, L/S of 4 ml·g-1 and stirring speed of 400 r·min-1, and under this acid leaching condition, the leaching rate of MgO was 97.24%. This process consumed a lot of sulfuric acid, but the leaching rate of MgO from boron mud had not been greatly improved. The optimized process conditions for acid leaching activated boron mud were acid leaching temperature of 95 ℃, time of 2.0 h, sulfuric acid concentration of 50%, L/S of 3 ml·g-1 and stirring speed of 400 r·min-1, and under this acid leaching condition, the leaching rate of MgO was 94.63%. Compared with unactivated boron mud, the leaching amount of MgO in the activated boron mud was increased by 20.80%; when the two leaching rates were similar, the amount of sulfuric acid was reduced by about 20%. Highly active MgO was produced during the activation process. Compared with MgCO3, it was easier to react with sulfuric acid. As CO2 escaped from the boron mud, it changed the surface morphology of the boron mud and made the acid leaching reaction easier. The activation treatment of boron mud was beneficial to the leaching of magnesium oxide, and it could also reduce the amount of sulfuric acid in the acid leaching process. © 2022, Youke Publishing Co., Ltd. All right reserved.
