Using Magnesium Reducing Slag To Produce Ca-Mg-Si Compound Fertilizer And Its Applied Basic Research

As an alkaline industrial waste, residue magnesium slag is usually treated as waste. It is not only waste these resources, but also caused certain environmental pollution. With the increasing global shortage of resources and environmental pollution problems, magnesium slag recycling utilization has become a main research direction for the sustainable development of magnesium industry, and it also become a research focus all over the world. Considering the magnesium slag is rich in the beneficial mineral elements to the crops, and most of the cultivated land in China is deficient element because of single fertilizating for a long time. This paper put forward a new technology of magnesium slag regenerated utilization, and did a series of research and analysis about it. The main results are as follows:(1) The research of physical and chemical characteristics of slag magnesium reduction. The microstructure, structure composition and thermal stability of magnesium slag was systematically characterized, and the results show that the chemical composition, physical and chemical properties and the content of harmful metals of magnesium slag are all accord with national fertilizer preparation standard. So it is feasibility to produce Si-Ca-Mg compound fertilizer by using magnesium slag. However, the form of silicon, calcium and magnesium element exist in the magnesium reduction slag are all undissolved salt, effective silicon content is low, so it needs to be activated.(2) Using magnesium reduction slag to prepare Si-Ca-Mg compound fertilizer and its basic research. First of all, the exiting types of available silicon in soil and its transformation form were analyzed. The effective silicon forms that can be absorbed by the plant are confirmed. Additionly, the physical and chemical performance of magnesium slag and its feasibility to prepared Ca-Mg-Si compound fertilizer is systematically analyzed. Based on the above research, the preparation of Ca-Mg-Si compound fertilizer process was designed.(3) The research of acid leaching magnesium reduction. The acid leaching of magnesium reduction slag could destruct the refractory silicate crystal structure, and realize the enrichment of amorphous SiO2 and water-soluble compounds of MgCl2, CaCl2 crystals. Acid leaching experiment parameter was optimized at the same time, and the optimal parameters are as follows: acid magnesium reduction slag is acid leached by 4 mol/L hydrochloric acid, under 25℃ within 120 min.(4) The effective silicon content of Si-Ca-Mg compound fertilizer was determined by silicon molybdenum blue colorimetric method. Firstly, the influence factors of effective silicon content determination were investigated. Considering the extent of the pH of the soil and crop root system environment, when the leaching agent is 100 mL 2% citric acid, the sample quality is 0.100 g and the vibration frequency is 180 r/min, the detection of effective silicon content is more reasonably and accurately. Secondly, the ratio of acid leaching residue to the crystallization product and calcine time was investigated by orthogonal test method. The optimized conditions are as follows : The ratio of acid leaching residue to the crystallization product is 1:0.25, auxiliary agent content is 3 %, calcine time is 240 min under the temperature of 500℃. The effective silicon content of prepared sample fertilizer can reach 29.78 %, which is up to national standards of silicon fertilizer.