LAUSR

Selective leaching of Na from red mud by using CaO with pressure leaching was investigated. The main factors studied were temperature, pressure, CaO dose, and leaching time. An L9(34) orthogonal test was carried out to analyze the importance of each factor and define optimal conditions. The leaching mechanism of sodium was investigated and analyzed using inductively coupled plasma–atomic emission spectrometry, x-ray diffraction, and scanning electron microscopy with energy-dispersive spectrometry. More than 85% of sodium could be dissolved under the optimal conditions. The order of influence of the investigated factors on the leaching efficiency of sodium was CaO dose > liquid-to-solid ratio > leaching time > leaching temperature/pressure. Cancrinite was decomposed from the red mud during the selective leaching process. The decomposition products silicon oxide and aluminum oxide reacted with calcium oxide, and the reaction products calcium silicate and calcium aluminate remained in the leaching residue. However, the other decomposition product, i.e., sodium oxide, was dissolved in the leaching solution. Other components in the red mud underwent almost no change in the process, representing an advantage compared with other processes that have been proposed.