Effects of process water recycling during flotation of copper and cobalt oxidised ores from Luiswishi deposit in the Democratic Republic of Congo

Laboratory flotation tests with copper–cobalt oxidized ore from the Luiswishi deposit in the
Katanga province were done using process water being recycled to different degrees. Grade
and recovery of copper and cobalt were followed by 10, 20 and 80% process to fresh water
addition with the results from these conditions being compared to those without water
recycling. When process water was recycled at 10%, 83.7% copper and 84.1% cobalt were
recovered at the rougher stage bringing the cleaner stage to a concentrate with recovery of
53 and 60% for copper and cobalt, respectively. However, recycling process water, up to 20
and 80%, has reduced the recovery of copper in the final concentrate to 23 and 6%, respectively,
and of cobalt to 46 and 27%, respectively. Monitoring of dissolved oxygen content,
pulp pH and Es potential during flotation, coupled with thermodynamic estimation of the
predominant chemical compounds in the system, has enabled to evaluate the effects on
flotation from the undesirable compounds’ formation during process water recycling. DRIFT
spectroscopy was used to identify the nature of the chemical compounds formed on malachite
and heterogenite surface during their sulphidisation in the presence of thiosulphate
ions. Thiosulphate ions depending on their concentration could promote or hinder malachite
and heterogenite flotation by inducing changes in pulp physicochemical parameters or
by altering mineral surface properties.