Experimental Determination of the Effect of CaO and Al2O3 in Slag Systems Related to the Conversion Process of High Copper Matte Grade

The slags generated in the conventional copper conversion process are mainly composed of Cu2O–Fe2O3–SiO2 with CaO, Al2O3, and MgO compounds—in concentrations up to 10 wt %. The present work contributes to the knowledge of the conversion process, generating experimental data for the phase diagrams of the Cu2O–Fe2O3–SiO2–Al2O3 and Cu2O–Fe2O3–SiO2–CaO systems. The experiments were carried out in a tubular furnace at temperatures of 1150 °C and 1200 °C, under a condition of saturation with tridymite and spinel. Once the equilibrium was reached, the samples were immediately quenched in water. The phases in the samples were observed through a scanning electron microscope (SEM) and the elemental composition of the phases were analyzed by means of energy-dispersive X-ray spectroscopy (EDS) detectors. The addition of Al2O3 and CaO into the Cu2O–Fe2O3–SiO2 system resulted in an appreciable displacement of the liquidus lines, corresponding to an expansion of the liquid in the tridymite primary phase field. The addition of CaO and Al2O3 combined was evaluated on industrial slags and from samples obtained in a Peirce–Smith furnace, with increasing amounts of CaO in the flux.

Induced Electro-Deposition of High Melting-Point Phases on MgO–C Refractory in CaO–Al2O3–SiO2 – (MgO) Slag at 1773 K

MgO–C refractory was polarized across the slag-refractory interface at a voltage of 8 V in a synthetic CaO–Al2O3–SiO2 – (MgO) Slag at 1773 K. A deposition layer mainly composed of dicalciumsilicate (2CaO.SiO2) or spinel (MgO.Al2O3) with several hundred microns thick was achieved by cathodic polarization. However, the anodic decay was accelerated in comparison to the cathodic refractories and nonpolarized reference MgO–C refractories. The electrodeposition layer was mainly caused by the reduction of silicate anions, in which a shift of slag composition to the dicalciumsilicate (C2S) or spinel (MA) primary phase field was induced. Furthermore, the rapid migration of mobile Ca2+ and Mg2+ ions can also lead to the enrichment of CaO and MgO at the slag/refractory interface. The present voltage level (8 V) is acceptable for the economic considerations and the slag component also need a careful section for the corrosion protection of MgO–C refractories.

Liquidus and phase equilibria in CaO-Al2O3-FeOx-SiO2 system under intermediate oxygen partial pressure

Phase equilibria of silicate slags relevant to the copper smelting/converting operations have been experimentally studied over a wide range of slag compositions, temperatures and atmospheric conditions. Selected systems are of industrial interest and fill the gaps in fundamental information required to systematically characterise and describe copper slag chemistry. The experimental procedures include equilibration of synthetic slag at high temperatures, rapid quenching of resulting phases, and accurate measurement of phase compositions using electron probe X-ray microanalysis (EPMA). The effects of CaO, Al2O3 and MgO on the phase equilibria of this slag system have been experimentally investigated in the temperature range 1200 to 1300 oC and oxygen partial pressures between 10-5 and 10-9 atm. It was found that spinel and silica are major primary phases in the composition range related to copper smelting/converting slags. In addition, olivine, diopside and pyroxene also appear at certain conditions. The presence of CaO, MgO and Al2O3 in the slag increases the spinel liquidus and decreases the silica liquidus. Liquidus temperatures in silica primary phase field are not sensitive to Po2; Liquidus temperatures in spinel primary phase field increase with increasing Po2. At 1300?C and low Po2, the spinel (Fe2+,Mg2+)O.(Al3+,Fe3+) primary phase field can be replaced by wustite (Fe2+,Mg2+)O.

Effects of CaO, Al2O3 and MgO on liquidus temperatures of copper smelting and converting slags under controlled oxygen partial pressures

Phase equilibria of silicate slags relevant to the copper smelting/converting operations have been experimentally studied over a wide range of slag compositions, temperatures and atmospheric conditions. Selected systems are of industrial interest and fill the gaps in fundamental information required to systematically characterise and describe copper slag chemistry. The experimental procedures include equilibration of synthetic slag at high temperatures, rapid quenching of resulting phases, and accurate measurement of phase compositions using electron probe X-ray microanalysis (EPMA). The effects of CaO, Al2O3 and MgO on the phase equilibria of this slag system have been experimentally investigated in the temperature range 1200 to 1300 oC and oxygen partial pressures between 10-5 and 10-9 atm. It was found that spinel and silica are major primary phases in the composition range related to copper smelting/converting slags. In addition, olivine, diopside and pyroxene also appear at certain conditions. The presence of CaO, MgO and Al2O3 in the slag increases the spinel liquidus and decreases the silica liquidus. Liquidus temperatures in silica primary phase field are not sensitive to Po2; Liquidus temperatures in spinel primary phase field increase with increasing Po2. At 1300 oC and low Po2, the spinel (Fe2+,Mg2+)O.(Al3+,Fe3+) primary phase field can be replaced by wustite (Fe2+,Mg2+)O.