Date of Award

2018

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering (PhD)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

Timothy C. Eisele

Committee Member 1

Julia A. King

Committee Member 2

Tony N. Rogers

Committee Member 3

Stephen A. Hackney

Abstract

The removal of excess phosphorus during the production of steel is vital for the production of strong, durable steel. Current processes focus on the removal of excess phosphorus during processing as molten iron with a basic oxygen furnace, utilizing a double slagging process which is expensive in time, capital costs, slagging reagents, and slag disposal. Removing phosphorus prior to steel production is the basis for this research. A method for the successful removal of phosphorus from iron ore is the application of sodium hydroxide (NaOH) in the evaporative leaching process at pH greater than 14, which is known to be capable of selectively leaching phosphorus from oolitic iron ores. The main limitation on implementing this leaching approach is the expense of NaOH. In order to make sodium hydroxide leaching practical, a method is needed for removing the dissolved phosphorus from solution and inexpensively regenerating the sodium hydroxide.

In this work, removal of phosphates from solution was achieved using calcium hydroxide (Ca(OH)2), which is significantly less expensive than NaOH. More importantly, the quantity of Ca(OH)2 depends on the mass of phosphorus present, not the total ore mass, and so the quantity used is only 1.2% of the ore mass. Up to 99.9% of phosphates in solution was removed within thirty minutes. A leaching comparison between fresh and regenerated caustic solution was performed applying the evaporative leaching technique, with removal rates of 79.0% and 75.9% respectively, demonstrating that the regenerated leaching solution was still effective for removing phosphorus. Implementing a countercurrent sodium hydroxide leaching circuit, coupled with a countercurrent precipitation process using calcium hydroxide reduces, and depending on the NaOH replenishment, eliminates costs and has the potential to create a profit of $1.22 per ton of ore.

Available for download on Sunday, December 01, 2019

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