Effluent treatment in IMI Phosphoric Acid Process

We present in this paper, in general terms, a description of the effluent treatment section of the IMI Phosphoric Acid Process that was developed by IMI. The IMI process, for production of high-grade technical phosphoric acid, involves the attack of phosphate rock by hydrochloric acid. It has been commercialized in Israel and in India. Process improvements and the need to reduce the quantity of solid waste produced by the Wet Phosphoric Acid Process to meet environmental regulations, have recently made the IMI process also attractive for fertilizer acid production. Five tons of phosphogypsum are formed for every ton of phosphoric acid produced by the Wet Phosphoric Acid Process, while the quantity of solid wastes in the IMI process is 10-15 times less. The paper includes: (a) a discussion of the effluents and the solids formed during the neutralization stage; (b) a presentation of effluent treatment results using different neutralizing agent combination; and (c) characteristic flow-sheets for the effluent treatment.