Effect of thiourea on sulphuric acid leaching of bastnaesite

The possibility of leaching bastnaesite pre-concentrate in dilute sulphuric acid solutions at 25 degreesC was studied, For this purpose, unroasted and roasted bastnaesite pre-concentrates were leached with 100 mL of 1-3 M H2SO4 and H2SO4 + thiourea solutions at 25 degreesC with a liquid/solid ratio of 20 mL/g for 6 h. Roasting affected the dissolution behaviour of rare earths in H2SO4 solution and dissolution of total rare-earth elements (REEs) was increased from 8.5% to 47.4%. The addition of thiourea to the leaching medium further increased the dissolution of the rare-earth elements in the unroasted and especially in the roasted preconcentrate due to the reduction of cerium (IV) to cerium (III) by thiourea, thus increasing the cerium dissolution value from 22.8% to 93.0%, which in turn increased the total dissolution of REEs from 17.6% to 89.0%. Thus, it was possible to precipitate 93.6% (CeO2 = 92.4%, La2O3 = 93.2%, Nd2O3 = 98.4%) of total REEs in the filtrate and the total REO content of the precipitate was determined as 92.6% (CeO2 = 58%, La2O3 = 29%, Nd2O3 = 5.6%). (C) 2003 Elsevier Science B.V. All rights reserved.