Leaching process of phosphorus and iron from steelmaking slag into malic acid solution

In order to remove phosphorus element from steelmaking slag and decrease iron loss, malic acid was selected as the leaching agent to dissolve steelmaking slag. Firstly, the influences of different factors, such as malic acid concentration, slag particle size, temperature, liquid/solid ratio and stirring speed, on the leaching ratios of phosphorus and iron were studied. Then, the kinetics for the leaching process of phosphorus was analyzed. The results showed that the leaching ratios of phosphorus and iron increase significantly with increasing the malic acid solution concentration and liquid/solid ratio. When the concentration of malic acid solution increases up to 0.01492 mol/L, about 80% phosphorus can be dissolved, and iron leaching ratio is less than 17%. In addition, decreasing slag particle size can obviously increase the leaching ratio of phosphorus. However, temperature and stirring speed have no significant effect on the dissolution of phosphorus and iron. The leaching kinetics of phosphorus follows the unreacted shrinking core model. Diffusion through product layer is the rate-limiting step of the leaching process, and the corresponding apparent activation energy is determined to be 3.32 kJ/mol. Finally, a semi-empirical kinetic equation was established.