Preparation of Magnesium Oxide and Potassium Magnesium Phosphate Cement From Lithium-Extracting Magnesium Slag

Abstract

MgO was prepared via washing to reduce the impurity of the ion content of the lithium-extracting magnesium slag, a by-product of the Salt Lake and obtained via the membrane separation method, followed by calcination. The MgO was used as a raw material to prepare magnesium potassium phosphate cement (MKPC). Through analyses including X-ray diffraction, scanning electron microscopy, hydration heat release rate, hydration products and porosity, the effects of the impurity of the ion content, and calcination temperature on the physicochemical and MKPC properties of MgO in the lithium-extracting magnesium slag were explored. The results show that the impurity of the ion content and calcination temperature only change the specific surface and crystal morphology of MgO, but not the basic phase composition. The optimal process for the preparation of MKPC from the lithium-extracting magnesium slag included washing to a filtrate the conductivity of 5000 μS•cm -1 and calcination at 1200 ℃. The MKPC prepared by this combination exhibited the longest setting time, the highest strength in the later stage, and no shrinkage. Regarding its microscopic morphology, the K-struvite structure had the largest size, most regular arrangement, and lowest porosity. This combination was also the most economical and met the requirement of low energy consumption.