Magnesium oxide is known as a green and safe wastewater treatment agent, this paper reviews the research and application progress of magnesium hydroxide in environmental protection, including the removal of heavy metal ions such as lead, chromium and nickel in industrial wastewater and the neutralization treatment of acidic wastewater, and lists the good treatment effect of magnesium hydroxide on some actual wastewater, including its treatment effect on some special wastewater such as boron-containing wastewater and radioactive wastewater, and finally outlooks its development prospect in production and application.
With the development of agriculture and industry and the expansion of urban scale, more and more wastewater containing heavy metal ions are discharged into the ecological environment, which has caused a series of environmental pollution problems.
In recent years, magnesium oxide, due to its large solubility area, can be used as adsorbent in water pollution treatment has shown a broad development prospect. The use of salt lake magnesium resources to produce magnesium oxide materials, not only can get a low cost, environmentally friendly, excellent adsorption performance of adsorbent materials, but also realize the high value utilization of salt lake magnesium resources, which brings double benefits for the environment and society. In the process of preparing magnesium oxide from magnesium chloride (MgCl2-6H2O), the precipitation crystallization method is widely used because of its low energy consumption, low cost and high yield, but the prepared magnesium oxide material often shows the disadvantages of uneven grain size, small specific surface area and poor adsorption performance.
The magnesium oxide was prepared by hydrothermal-calcination method and carbonization-calcination method using industrial magnesium hydroxide as raw material. In the former method, the raw material magnesium hydroxide was prepared as hexagonal flake magnesium hydroxide by hydrothermal, and then calcined at appropriate temperature to obtain active magnesium oxide; in the latter method, Mg(OH)_2 was firstly converted into lamellar flower-like alkali magnesium carbonate or magnesium carbonate whisker trihydrate as precursors by CO_2, and then highly active magnesium oxide was obtained by calcination. The effects of precursors, calcination temperature and calcination time on the activity of MgO were investigated. The results showed that the MgO prepared from MgCO_3-3H_2O whiskers exhibited excellent activity with a citric acid value of 8.45s and an iodine uptake value of 262.14 mg-g~(-1). The adsorption performance of the prepared active MgO on Pb~(2+) was investigated and showed good adsorption on Pb~(2+) with a saturation adsorption capacity of 364 mg-g~(-1), and the process was in accordance with the Langmuir adsorption model.