Ammonium sulphate as promoting agent of the sulphidization process of oxidized Cu-Co ores from the Luiswishi deposit (RDC)

The Luiswishi deposit belongs to the Cu-Co deposits of the Southern Group of the Katangian Copper Belt and is operated by a joint venture between EGMF (Entreprises Générales Malta Forrest) and Gecamines (Générale des Carrières et des Mines). The Cu-Co ore is beneficiated by the sulphidization process at the NCK (New Concentrator of Kipushi) at Kipushi.
Sulphidization followed by flotation with sulphydryl collectors is a common practice for the treatment of oxidized base metals ores. This process is complex and its application at the industrial scale is quite sensitive. In Central Africa it is also a cost intensive treatment as the sulphidizing agent has to be imported. In order to improve the metallurgical performances and to optimise the economics of the process, a laboratory research program was carried out by the Laboratory of Metallurgy and Mineral Processing (MTM) of the University of Liège in close collaboration with EGMF and Gecamines. This program included the study of various flotation reagents as dispersing, depressing and activating agents.
This paper presents the results obtained with the use of ammonium sulphate as activator of the sulphidized xanthate flotation. Although ammonium sulphate has been mentioned in the literature as a promoting agent of the sulphidized xanthate flotation of malachite, its effects on the flotation of cobalt oxides was not known.
The testworks were carried out on various oxidized siliceous ore types from the Luiswishi deposit. A 1.7 l Agitair laboratory flotation cell was used. NaHS and potassium amylxanthate were respectively choosen as sulphidizer and collector. A mixture of gasoil and tall oil (90/10) was used as secondary collector. A multistage sulphidization was realised. Values of pH were followed during the different tests and an ion selective electrode Ag/Ag2S was used to control the Es potentiel evolution during the stepwise addition of the sulphidizer.
The addition of ammonium suphate [(NH4)2SO4] simultaneously with NaHS led to the following results:
-A marked improvement of the sulfidization kinetics leading to shorter conditioning times and limiting the number of sulphidizing stages required to reach maximum recoveries.
-The inhibition of the depressive effect on Cu and Co flotation of an excess of hydrosulphide ions in the pulp.
-An improvement of the selectivity of the flotation combined with higher cobalt recoveries. The promoting effect is indeed more effective for cobalt than for copper and cobalt recoveries were improved by 4 to 8 %.
-A significant decrease of the sulfidizer consumption.
These laboratory results were implemented at an industrial scale at the NCK at Kipushi. In close accordance with the laboratory results the sulphidization kinetics were improved and the cobalt recoveries rose by 7 % while maintaining the previous Cu and Co grades of the concentrate.
Ammonium sulphate being a low cost and common reagent (it is easily found in the fertiliser industry or as a byproduct of the coke industry), its use significantly improved the economics of the flotation of Cu-Co oxides ores from the Luiswishi deposit.