Green liquor dregs (GLD), a residual product from sulfate paper mills, was blended with tailings, fly ash, and bark sludge with the aim of improving the material’s physical properties so that it could function as a sealing layer in dry covers on sulfidic mine waste. Geotechnical and geochemical investigations, including weathering cell tests, were carried out on GLD with admixtures to assess their effectiveness. Due to its alkaline character, GLD was shown to have the potential to improve leachate quality by decreasing metal mobility when blended with tailings. The admixtures showed favorable sealing layer properties such as high water retention capacity and low hydraulic conductivity. However, caution must be exercised when the dregs are blended with tailings containing large amounts of As and Mo, since increased leaching of these elements may be expected.

The influence of major components of calcium and sulfate ions in process water on xanthate collector adsorption and flotation response of pure chalcopyrite, galena, and sphalerite minerals was investigated by Hallimond tube flotation, zeta-potential, FTIR, and XPS spectroscopy studies, while bench scale flotation tests were also carried out using complex sulfide ores. Marginally lower recoveries of chalcopyrite and galena in process water and in the presence of calcium and sulfate ions in both deionized and process waters using potassium amyl xanthate as collector were observed in Hallimond tube flotation, whereas sphalerite floatability is a little increased in process water using isobutyl xanthate as collector. Zeta-potential results show the adsorption of calcium ions on the minerals. FTIR and XPS studies revealed the presence of surface oxidized sulfoxy species and surface calcium carbonates and/or calcium sulfate on chalcopyrite and galena in the presence of process water and water-containing calcium ions at flotation pH 10.5, and these surface species influenced xanthate adsorption. Surface-oxidized sulfoxy and carbonate species were seen on sphalerite surface in the presence of deionized water, process water, and water-containing calcium and sulfate ions at pH 11.5, but the surface species does not influence xanthate adsorption. Bench scale flotation using two different complex sulfide ores showed that chalcopyrite, galena, and sphalerite recoveries are higher in process water than tap water and general decrease of the minerals floatability at temperatures lower than 22°C in either tap water or process water

An approach to environmental sustainability and improved process economy in sulphide minerals production is recycling of process water in flotation of complex sulphide ores. However process water chemistry may be a critical issue to flotation efficiency. Process water discharged from sulphide flotation circuits are usually gypsum (CaSO4.H2O) saturated and have a high salinity. The major ionic species contained in the process water are Ca2+ and SO42- ions. As minor species, they commonly contain reduced sulphur compounds (RSC) (sulfoxyanions with sulphur in the oxidation state below (VI) such as SO32-, S2O32-, S2O52-, and S4O62-), cations of ferrous and non-ferrous metals, frothing molecules, residual chemical reagents and products of their degradation. However, the key step towards developing scientific approaches of recycling the process water is elucidation of how, in what extent, and why the recycled water components (taken singly or jointly) influence flotation of sulphides.Therefore a research program was initiated to understand the influence of the major and minor process water species on flotation and how to flexibly control such effects if any. In this work, the influence of major components of calcium and sulphate ions in process water on flotation of chalcopyrite, galena, sphalerite and pyrite minerals were investigated by Hallimond tube flotation. The surface chemistry and xanthate collector adsorption on the minerals under the influence of process water species were also studied by zeta-potential measurement, Fourier transform infrared spectroscopy (FTIR) with diffuse reflectance attachment and Xray photoelectron (XPS) spectroscopy. The effects of the major components were also investigated on complex sulphide ores flotation using bench scale flotation equipment. The impact of the species in flotation was studied using deionised water, tap water, process water and simulated water containing equivalent amount of calcium and sulphate species in process water.Oxidation of sulphide minerals has been known to be a very critical issue during flotation of sulphide minerals while several authors had reported that pyrite, the most abundant metal sulphide and very common gangue mineral in sulphide ores can generate hydrogen peroxide (H2O2). Hydrogen peroxide is a strong oxidizing agent stronger than oxygen. It was revealed that ferric defects on ground pyrite surfaces can generate OH• radicals upon interaction with water and combination of two OH• radicals yields H2O2. However, participation of these species in non-selective oxidation of the sulphide ore pulp components and hence in deteriorating the concentrate grade and recovery of metal-sulphides has not still been explored yet. In an attempt to fill the gap, a preliminary study was done to estimate the concentration of H2O2 in a complex sulphide ore pulp liquid during different times of ore grinding and compare them to oxidation of pulp solid. Study of possible ways of flexibly controlling H2O2 formation through known chemical means was also attempted.Hallimond tube flotation results showed marginally lower recoveries of chalcopyrite and galena in process water and in the presence of calcium and sulphate ions in both deionised and process waters using potassium amyl xanthate as collector. Whereas sphalerite and pyrite floatability were little increased in process water. There is no significant effect of calcium and sulphate ions on sphalerite in deionised water using isobutyl xanthate as collector. Zeta-potential shows the adsorption of calcium ions on the minerals whereby the potential are seen to increase, while sulphate ions have no significant effect. FTIR and XPS studies revealed the presence of surface oxidised sulfoxy species and surface calcium carbonates and/or calcium sulphate on chalcopyrite in the presence of process water and water containing calcium ions. Surface oxidised sulfoxy and carbonate species were seen on galena in the presence of deionised water, process water and water containing calcium and sulphate ions. The studies also showed hydrated surface oxidised species and surface iron and calcium carbonates on pyrite in the presence of process water and water containing calcium ions all at flotation pH 10.5. These surface species influenced xanthate adsorption on chalcopyrite, galena and pyrite. The presence of surface oxidised sulfoxy and carbonate species at the sphalerite flotation pH 11.5 were seen in the presence of deionised water, process water and water containing calcium and sulphate ions, but the surface species does not influence xanthate adsorption.Formation of hydrogen peroxide was revealed during grinding of a complex sulphide ore for the first time in mineral processing application and its formation was reduced by diethylenetriamine (DETA). FTIR spectroscopy of the pulp solid fraction shows varying degree of oxidised surface species which is related to concentration of H2O2 analyzed in pulp liquid. Addition of DETA at low concentration during grinding of complex sulphide ore depresses iron and copper minerals flotation during copper-lead flotation stage, DETA also depresses iron minerals during zinc mineral flotation. Consequently copper minerals flotation to copper-lead products is reduced and they are reporting to zinc products. However zinc minerals flotation to zinc product is improved.Tests performed on two different complex sulphide ores using bench scale flotation equipment showed that chalcopyrite, galena and sphalerite minerals recoveries are better in process water than tap water. The results also showed general decrease of the minerals floatability at temperatures lower than 22oC in either tap water or process water. An analysis of pulp liquid after flotation shows decreased calcium and increased sulphate ions. This indicates that there is adsorption of calcium ions on the minerals and dissolution and release of sulphate ions in solution. The studies showed that the process water can be recycled in flotation with no significant effect on grade and recovery of sulphide minerals.

Large variations in flotation characteristics of minerals have been observed in winter and summer in plant practices as a result of changes in pulp temperature. Variations in temperature may affect the quality for pulp and related process water through changes in dissociation of different chemical species within the pulp, as well as changing in gas and metal hydroxide solubility, reagent adsorption and its stability on mineral surfaces, water/pulp viscosity, etc. All of these affect the flotation characteristics of specific mineral to some degree or another. It has been observed in Cu-Pb-Zn and/or Pb-Zn sulfides flotation that sphalerite (ZnS) flotation is strongly affected by changes in pulp temperature. Plant practices have shown that at the both low, e.g., T <10-12°C, and high, e.g., T > 60°C, the recovery for copper activated sphalerite is dramatically dropped. Within this paper the effect of pulp temperature on flotation characteristics of sphalerite is brought into considerations and laboratory flotation tests were conducted in conjunction with surface and solution chemistry analysis to understand the effect of temperature on sphalerite recovery. The effect of temperature seems to be complex since the temperature affects both the physical (hydrodynamics) and chemical phenomena in the flotation cell. In fact all sub-processes in flotation, i.e., collision, attachment and detachment, are affected by changing in temperature. Experimental results indicating that at alkaline pH values, e.g., 8.5 to 10.5, the recovery for copper-activated sphalerite is dramatically reduced when temperature is below 10-12°C, which is in agreement with plant practice at Boliden's Garpenberg plant in Sweden. However, results from other studies indicated that the zinc recovery is also considerably decreased at high pulp temperatures, i.e., 62°C and above.

The effects of major components of calcium and sulphate species present in recycled process water on galena flotation has been investigated through Hallimond flotation, zeta-potential, diffuse reflectance FTIR spectroscopy and XPS measurements using pure galena mineral. The significance of process water species in flotation has been understood using deionised water, process water and simulated tap water containing equivalent calcium and sulphate ions concentration as in process water.Hallimond flotation indicated marginally lower recoveries of galena in the presence of calcium and sulphate ions using potassium amyl xanthate as collector. Zeta-potential shows the adsorption of calcium ions whereby the potential are seen to increase while sulphate ions have no significant effect. FTIR and XPS studies revealed surface calcium carbonate and/or calcium sulphate species in process water which affected xanthate adsorption. Presence of surface oxidised species such as sulfoxy, hydroxyl species on galena at pH 10.5 in deionised and process water was also revealed.

An approach to environmental sustainability and improved process economy, in sulphide minerals production is recycling of process water in flotation of complex sulphide ores, although the chemistry of process water may be a critical issue to flotation efficiency. The influence of major components of calcium and sulphate ions in process water on xanthate collector adsorption and flotation response using pure chalcopyrite, galena and sphalerite minerals were investigated by Hallimond flotation, zeta-potential measurement, FTIR and XPS spectroscopy studies, while bench scale flotation tests were also carried out using complex sulphide ores. The impact of the species in flotation was comprehended using deionised water, tap water, process water and simulated water containing equivalent amount of calcium and sulphate species in process water. Hallimond flotation results showed a decrease of chalcopyrite and galena recovery in process water and also in the presence of calcium and sulphate ions in both deionised and process waters, whereas sphalerite does not respond to flotation. The adsorption of calcium and metal ions but not sulphate ions on the minerals is evidenced by zeta-potential data. FTIR and XPS studies revealed the presence of surface oxidized sulfoxy species and surface calcium carbonates on chalcopyrite in the presence of process water and water containing calcium ions, surface oxidized sulfoxy and carbonate species on galena in the presence of deionised water, process water and water containing calcium and sulphate ions, all at flotation pH 10.5, and these surface species influenced xanthate adsorption. The presence of surface oxidized sulfoxy and carbonate species at the sphalerite flotation pH 11.5 were seen in the presence of deionised water, process water and water containing calcium and sulphate ions, but the surface species does not influence xanthate adsorption. Bench scale flotation using two different complex sulphide ores showed that chalcopyrite, galena and sphalerite recoveries are better in process water than tap water. The studies showed that the process water can be recycled in flotation with no detrimental effect on grade and recovery of sulphide minerals.

In order to predict and minimize detrimental production problems due to the recycling of process water in sulfide ore processing, the influence of major species, calcium and sulfate in process water on sphalerite flotation was investigated through Hallimond tube flotation, zeta potential, diffuse reflectance Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements using sphalerite mineral sample. Assessment of process water species in flotation was done using deionized water, process water and simulated water containing calcium and sulfate ions in experiments. Hallimond flotation shows increased sphalerite floatability in process water compared to deionized water, but no significant effect on the presence of calcium and sulfate ions in deionized water using isobutyl xanthate as a collector. The presence of calcium ions reduced the sphalerite's negative zeta potential, while at higher concentrations, a charge reversal occurred, at about pH 11. FTIR and XPS studies revealed the presence of surface-oxidized sulfoxy and carbonate species on sphalerite at pH 11.5 in deionized water, process water and water containing calcium and sulfate ions. These surface species do not influence xanthate adsorption.

Hydrogen peroxide production was measured during the grinding of a complex sulfide ore, and its oxidizing effect on solid surfaces was investigated using Fourier transform infrared spectroscopy (FTIR) with diffuse reflectance attachment measurement. In turn, an attempt was made to correlate the formation of hydrogen peroxide, surface oxidation and sphalerite flotation. Additionally, in order to predict and minimize detrimental production problems due to the recycling of process water in sulfide ore processing, the effects of major components of calcium and sulfate species present in recycled process water and the effect of temperature on sphalerite flotation were investigated through bench-scale flotation tests using complex sulfide ores. The significance of process water species in flotation was studied using tap water, process water and simulated water containing calcium and sulfate ions. Formation of hydrogen peroxide was revealed during the grinding of the complex sulfide ore, and its formation was counteracted by diethylenetriamine (DETA). The FTIR spectrum of the pulp solid fraction showed varying degrees of oxidized surface species, which are related to the concentration of H2O2 analyzed in pulp liquid. Bench-scale flotation using two different complex sulfide ores showed that sphalerite recovery is better in process water than in tap water. Flotation results also indicated a varied recovery of sphalerite at different temperatures in either tap water or process water.