Analysis of copper losses throughout weak acid effluent flows generated during off-gas treatment in the New Copper Smelter RTB Bor

Association of Metallurgical Engineers of Serbia AMES Scientific paper UDC: 628.161.2:546.561 ANALYSIS OF COPPER LOSSES THROUGHOUT WEAK ACID EFFLUENT FLOWS GENERATED DURING OFF-GAS TREATMENT IN THE NEW COPPER SMELTER RTB BOR Dragana Ivšić-Bajčeta1∗, Željko Kamberović2, Jelena Rogan2, Milorad Ćirković3, Toplica Pavlović4 1 Innovation Center of the Faculty of Technology and Metallurgy in Belgrade, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia, 2 Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia 3 Mining and Metallurgy Institute Bor, Zeleni bulevar 35, 19210 Bor, Serbia 4 Megatrend University in Belgrade, Goce Delceva 8, 11070 Novi Beograd, Serbia Received 08.04.2013 Accepted 18.07.2013 Abstract The previous inadequate treatment of off-gas in RTB Bor in Serbia has resulted in serious pollution of the environment and the possibly high losses of copper through the effluent flows. The project of New Copper Smelter RTB Bor, besides the new flash smelting furnace (FSF) and the reconstruction of Pierce-Smith converter (PSC), includes more effective effluent treatment. Paper presents an analysis of the new FSF and PSC off-gas treatment, determination of copper losses throughout generated wastewaters and discussion of its possible valorization. Assumptions about the solubility of metals phases present in the FSF and PSC off-gas, obtained by the treatment process simulation, were compared with the leaching results of flue dusts. Determined wastewaters characteristics indicate that the PSC flow is significantly richer in copper, mostly present in insoluble metallic/sulfide form, while the FSF flow has low concentration of copper in the form of completely soluble oxide/sulfate. The possible scenario for the copper valorization, considering arsenic and lead as limiting factors, is the separation of the FSF and PSC flows, return of the metallic/sulfide solid phase to the smelting process and recovery from the sulfate/oxide liquid phase. Keywords: Copper smelter, off-gas treatment, arsenic, lead. ∗ Corresponding author: Dragana Ivšić-Bajčeta, 217 Metall. Mater. Eng. Vol 19 (3) 2013 p. 217-231 Introduction RTB Bor in Serbia is an integrated copper mining and smelting complex considered to be one of the most important producers of copper and precious metals in Central Eastern Europe. Active copper production in RTB Bor, dating since 1903, was accompanied by devastation of the resources and the environment (pollution of water, air and soil, low level of energetic efficiency) [1]. The reduction of liquid and gaseous effluents is expected after the completion of modernization and reconstruction project in late 2013/ spring 2014 [2]. The Project includes replacement of the old roaster/reverberatory furnace with more efficient autogenous smelting of sulfide concentrates in a floating state - Outokumpu Flash Smelting Furnace [3]. RTB Bor has been waiting for autogenous smelting technology for over 70 years since the first initial tests of concentrate smelting to matte and slag without fuel were conducted in the same RTB Bor (former Société Française des Mines des Bor) just before the World War II [4]. The pyrometallurgical copper extraction in the New Copper Smelter RTB Bor from sulfide concentrate (CuFeS2, FeS2, Cu2S and FeS) will consist of concentrate drying, autogenous smelting in a flash smelting furnace (FSF) and matte converting process in a Pierce- Smith converter (PSC). The products of copper sulfide concentrate smelting in the FSF are (i) molten sulfide matte (62% Cu), (ii) molten oxide slag (1.4% Cu) and (iii) off-gas (32.3% SO2). Main oxidation reactions occurring in the FSF are [5]: 13 1 3 5 (1) 2CuFeS2 + O2 ( g ) → Cu2 S ⋅ FeS + FeO + SO2 ( g ) 4 2 2 2 matte in off-gas (2) 2 FeO + SiO2 → 2 FeO ⋅ SiO2 slag The process of matte converting takes place in the PSC during two periods [5] (i) the FeS elimination, the “slag blow” period: (3) 2 FeS + 3O2 ( g ) + SiO2 → 2 FeO ⋅ SiO2 + 2SO2 ( g ) slag in off-gas (ii) the blister copper forming, the “copper blow” period: (4) Cu2 S + O2 ( g ) → 2Cu 0 + 2SO2 ( g ) blister in off gas copper Generation of SO2 during the FSF and PSC processes is essential disadvantage of conventional copper extraction from sulfide ores [6]. Beside SO2, off gas may also carry substantial levels of copper and impurities (such as arsenic, zinc, lead, bismuth and iron) in the form of dust and volatile phase. Previous inadequate treatment of off-gas in RTB Bor resulted in sever environmental pollution [7, 8], as well as potentially high copper losses. In order to increase process efficiency and reduce environmental impact, the New Copper Smelter RTB Bor will include more efficient treatment of off-gas and its further processing in a sulfuric acid plant (SAP). The FSF off-gas is treated in the waste heat boiler (WHB) and the electrostatic precipitator (ESP). During cooling in the WHB the oxide flue dust, suspended in SO2 off-gas, will transform to sulfates: Bajčeta at al. - Analysis of copper losses throughout weak acid effluent flows ... 1 MeO + SO2 ( g ) + O2 ( g ) → MeSO4 2 219 (5) Flue dust from the FSF recovered in the WHB and ESP will be re-circulated to the smelting process. Off-gas from the ESP is transported to wet scrubber and cooling tower for wet gas cleaning. The solution from the scrubber and liquid phase formed during condensation in the cooling tower for the FSF off-gas treatment are the first source of weak acid effluent from the New Copper Smelter. The off-gas that exits the PSC will be cooled and treated in an evaporative cooling chamber (ECC). Dust collected in the ECC will be returned to the smelting process. Similar to the FSF wet gas cleaning, off-gas from PSC, will be further cooled and treated in a wet scrubber and a cooling tower. The purified FSF and PSC gases from cooling towers are mixed and sent to a wet electrostatic precipitator (WESP). Suspension created in the scrubber and cooling tower for the PSC off-gas and liquid formed in the WESP represent the second source of weak acid effluent from the New Copper Smelter. Technological scheme of the New Copper Smelter and off-gas cleaning processes is presented in Fig. 1. Generated weak acid effluents represent wastewaters from the copper smelter that will be processed in an effluent treatment plant (ETP). These wastewaters are characterized by high content in free sulfuric acid and heavy metals such as Cu, Ni, Zn, Fe, Pb, As, Bi, and Sb [9]. In the ETP, the FSF and PSC wastewaters will be neutralized with lime while heavy metals will precipitate as hydroxides and form wastewater treatment sludge [10]. Copper and other valuable metals collected in the wastewater treatment sludge represent irreversible loss from the copper smelting process. Fig. 1. Technological scheme of the New Copper Smelter and off-gas cleaning processes 217 Metall. Mater. Eng. Vol 19 (3) 2013 p. 217-231 The aim of the presented study wa (...truncated)