CONTROL OF UNDESIRABLE URANIUM LEACHING IN A PRIMARY MINERAL PROCESSING CIRCUIT

S. Humphrey1, T. Byrne1, J. Gogal1, M. Davoodi1, D. Kao2

1 Cameco Corporation, Cigar Lake Operation; 2121 – 11th Street West, Saskatoon, Saskatchewan. S7M 1J3.

2 University of British Columbia; 2329 West Mall, Vancouver, B.C. V6T 1Z4.

ABSTRACT

High total and dissolved uranium values were noted in the process water at the Cigar Lake Operation (CLO) during production start-up, whereas significant levels of dissolved uranium had not been observed previously at other similar operations. The excess dissolved uranium resulted in higher demands on the mine water treatment plant, along with higher operating costs, and some unrealized revenue potential. A species balance indicated that uranium was leaching into solution in the grinding, dewatering, and storage circuits under normal operating conditions. Jet boring, ball milling, and the use of Pachuca tanks for ore storage result in a highly oxidative environment which is favourable to leaching.

This paper will outline the testwork performed to identify the conditions under which the uranium leaches into solution and to determine required conditions for precipitation. Maximum uranium leaching was found to occur under normal operating conditions (pH ranging from 7 to 8); testwork indicated that both lowering and raising the pH can significantly reduce the uranium leaching.

Analytical results combined with the batch scale testwork indicate that the uranium solubility is associated with carbonate species in the ore. Uranium precipitation was maximized at pH values greater than 10.5 or less than 6, corresponding well to carbonate leaching and precipitation values from literature. Higher precipitation efficiencies were noted at high pH ranges.

As a result of this work, a pH control system has been recommended for implementation in the Pachuca storage vessels and thickener prior to water treatment plant. Caustic soda is recommended for pH control due to material requirements and downstream constraints.

KEYWORDS

Uranium, leaching, precipitation, carbonates, grinding