Feasibility of manufacturing phosphoric acid by smelting reduction technology

Abstract

In this paper, a new process for directly making phosphoric acid from phosphorus ore by smelting reduction with postcombustion is presented based on the experience in smelting reduction for iron-making. Theoretically, the new process can save energy when compared with the traditional pyro-process for the manufacture of phosphoric acid. Laboratory simulation shows that it is possible to make phosphoric acid by smelting reduction with postcombustion process. Fundamental research on phosphate reduction in molten slag is carried out. Experimental results show that the reduction rate increases with the increase of temperature, basicity of slag, and stirring intensity of the molten slag. Carbon dissolved in the liquid Fe–P–C alloy has a greater reduction potential than solid carbon. Under the condition of slag basicity (CaO/SiO₂) equal to 1˙1, and the concentration of Al₂O₃ at 8˙3%, the reduction rate constant by solid carbon can be expressed as k = 1˙1 × 10³ exp(–217 360/RT). The rate constant for reduction by carbon in liquid Fe–P–C alloy is about 10 times larger than that for solid carbon under similar conditions. The reduction by bubbling CO gas is close to the thermodynamic equilibrium assuming that bubbles escape from the slag bath.