Recovery of yttrium from deep-sea mud

Abstract

Deep-sea mud rich in rare earth yttrium has received lots of attention from the international community as a new resource for Y. A novel process, which mainly includes acid leaching, solvent extraction, and oxalic acid precipitation-roasting, is proposed for recovery of Y from deep-sea mud. A series of experiments were conducted to inspect the impacts of various factors during the process and the optimum conditions were determined. The results show that the Y of deep-sea mud totally exists in apatite minerals which can be decomposed by hydrochloric acid and sulfuric acid solution. The highest leaching efficiency of Y is 94.53% using hydrochloric acid and 84.38% using sulfuric acid under the conditions of H+ concentration 2.0 mol/L, leaching time 60 min, liquid–solid ratio 4:1 and room temperature 25 °C (only in case of sulfuric acid, when using hydrochloric acid, the leaching temperature should be 60 °C). Because of the much lower leaching temperature, sulfuric acid leaching is preferred. The counter current extraction and stripping tests were simulated by a cascade centrifugal extraction tank device. Using 10 vol% P204, 15 vol% TBP and 75 vol% sulfonated kerosene as extractant, 98.79% Y3+ and 42.60% Fe3+ are extracted from sulfuric acid leaching liquor (adjusted to pH = 2.0) after seven-stage counter current extraction with O/A ratio of 1:1 at room temperature, while other metals ions such as Al3+, Ca2+, Mg2+ and Mn2+ are almost not extracted. The Y3+ in loaded organic can be selectively stripped using 50 g/L sulfuric acid solution and the stripping efficiency reaches 99.86% after seven-stage counter current stripping with O/A ratio of 10:1 at room temperature, while only 2.26% co-extracted Fe3+ is stripped. The Y3+ of loaded strip liquor can be precipitated by oxalic acid to further separate Y3+ and Fe3+. The precipitation efficiency of Y3+ in loaded strip liquor can be 98.56% while Fe3+ is not precipitated under the conditions of oxalic acid solution concentration 200 g/L, quality ratio of oxalic acid to Y of 2, and precipitation time 0.5 h. And the precipitate was roasted at 850 °C for 3 h to obtain the oxide of Y in which the purity of Y2O3/REO is 79.02% and the contents of major non-rare earth impurities are less than 0.21%. Over the whole process included acid leaching, solvent extraction, and oxalic acid precipitation-roasting, the yttrium yield is 82.04%.