Effect of Si Ion Concentrations on the Phosphorous Ion Separation from the Solution Containing Ca, Si, and P Ions by Ion-exchange Membrane Electrodialysis

Phosphorus is an essential raw material for industry and agriculture, and Japan imports all of it. The phosphorus in steelmaking slag is a promising secondary phosphorus resource comparable to the total amount of phosphorus imported by Japan. Several processes have been proposed to recover phosphorous from steelmaking slags. However, due to the high recovery cost and high environmental load in these processes, phosphorus recovery from steelmaking slag is not yet practiced on an industrial scale. We are developing an electrodialysis process for recovering phosphorus from steelmaking slag extract. Steelmaking slag extract contains not only P anions but also Si anions. This paper has investigated the influence of Si ions on phosphorus separation by electrodialysis. In the case of a solution containing more than 50 ppm of Si content, it was found that Si ions significantly inhibit the transport of phosphorus ions through the membrane.