The Detrimental Impact of High Pulp Temperature on Sphalerite Flotation After Zinc Regrinding in the Zinc Plant of Somincor, Lundin Mining Corporation, Neves Corvo, Portugal

This paper focuses on the impact of high pulp temperature on sphalerite flotation after the zinc regrind circuit in the Zinc Plant of Somincor, owned and operated by Lundin Mining Corporation. In the zinc circuit, the zinc rougher concentrate is reground with forged steel media before flotation with one stage of roughing and scavenging, and three stages of cleaning to obtain a zinc final concentrate (zinc grade >50 per cent). After regrinding, sphalerite flotation has been found to be seriously affected by high pulp temperature which may occur during the summer months. Mineral recoveries were found to be seriously reduced at pulp temperatures above 60¦C. At this high pulp temperature, neither elevated copper sulfate concentration nor a decreased pH alone appreciably increased Zn recovery. However, a combination of these two (eg a decrease in pH from 11.5 to 10.8, and an increase in copper sulfate dosage from 400 g/t to 800 g/t) was found to reduce Zn depression at high pulp temperature. At pulp temperatures below 45¦C, the negative influence of pulp temperature on mineral recoveries was minimal. A systematic series of flotation tests and solution/surface analyses were performed to reveal causes for poor sphalerite flotation at high pulp temperature after regrinding. The decrease in mineral recovery was shown to be associated with variations in the surface species on mineral particles in response to the increased pulp temperature. These variations in the surface species include collector desorption and superficial oxidation to form lead/zinc oxide/hydroxides on mineral particles. The influence of the type of regrinding media on sphalerite flotation at high pulp temperature was also addressed in this work.