Solidification of Waste Hydrofluoric Acid Raffinate from Tantalum Refining
As the first step in production of tantalum, the ore is dissolved in hydrofluoric acid (HF). The acid is then extracted with an organic solvent to isolate the tantalum fluoride salt. Raffinate, the spent 15% HF after extraction, contains half of its fluorides as complex anions of iron, silicon, niobium, and other rare earth elements. Historically, Cabot Supermetals, Inc. treated raffinate with other process wastewaters by alkaline precipitation with lime. The effluent from this process would not reliably meet proposed NPDES Permit limits for fluoride, some metals, and contributed to elevated effluent Total Dissolved Solids (TDS). After piloting, Cabot adopted raffinate solidification with lime (calcium oxide, CaO) to achieve discharge permit compliance. This paper presents the design criteria, equipment and operating results.
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Document Type: Research Article
Publication date: 2008-01-01
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