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Characterization and Recovery of Copper from Smelting Slag

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Characterization and Recovery of Copper from Smelting Slag CHARACTERIZATION AND RECOVERY OF COPPER FROM SMELTING SLAG A. P. GABRIEL*, L. R. SANTOS*, A.C. KASPER*, H. M. VEIT* * Materials Engineering Department, Engineering School, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazi SUMMARY: 1. INTRODUCTION. 2. EXPERIMENTAL. 2.1 Hazardousness test. 2.2 Chemical and mineralogical characterization. 2.3 Leaching 3. RESULTS AND DISCUSSION 3.1 Hazardousness Test. 3.2 Chemical and mineralogical characterization. 3.3 Leaching. 4. CONCLUSION. REFERENCES. 1. INTRODUCTION The generation of industrial solid waste constitutes an environmental problem that requires efforts for adequate disposal. Currently, in Brazil, solid waste management is standardized, with a classification determining the management according to its hazardous characteristics. ABNT NBR 10004 is a Brazilian Standard to solid waste and classifies its as: Class I (hazardous), Class II - A (non - hazardous and non - inert) and Class II - B (non - hazardous and inert) according to the concentration of elements that have potential risks to the environment and public health (ABNT NBR 10,004, 2004) A process with a large generation of wastes is the production of copper. Several studies in the last decades investigated routes to recovery copper and other metals of interest from the slag (solid waste from the foundry). In the case of primary production, the slag has copper contents between 0.5 and 2% and the volume generated is twice the refined metal (Schlesinger et al., 2011) In addition to primary copper production, there is a significant rate of the copper production from scrap/waste metal. Secondary copper production in Brazil in 2014 reached 23,600 tons, representing around 9% of domestic production. This secondary slag presents, due to its great generation, the potential to be recycled as a secondary source of copper (Departamento Nacional de Produção Mineral, 2016) Copper is a metal of high value and of great importance for several industrial sectors, especially the electrical and electronic sector, due to its properties such as excellent conductivity and resistance to corrosion. However, obtaining copper from ores requires high energy resources, have great environmental impacts, besides what, the existing mines have lower copper contents, between 1 and 2%, which makes the extraction more expensive (Schlesinger et al. 2011). On the other hand, the copper recycling process allows to obtain a material with the same properties as obtained by the primary extraction, not involving great complexity, being basically a fusion process and later refined by pyrometallurgy or electrolysis. In the recycling process, during the smelting stage, there is the generation of waste, especially a secondary slag with high levels of copper. In the secondary slag it is estimated that the copper content is high, because the input is Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 basically copper, with characteristic impurities of the scrap, but predominantly the metal is concentrated, which makes this residue very attractive for recovery of copper. The extraction of metals from the foundry slag has several studies using leaching at atmospheric pressure using different leaching agents such as acids, bases and salts (Albrecht et al., 2004), and also with the use of high pressures in oxidative leaching (Curling et al., 2004; 2007, Li et al., 2008, 2009;). Banza et. al (2002) studied the recovery of copper from a primary copper smelter slag using sulfuric acid with hydrogen peroxide, obtaining a recovery of about 95% copper. Abdel Basir et. al. (1999) and Ahmed and Nayl (2016) evaluated the recovery of copper from brass smelter slag, with copper contents averaging 20%, using leaching with sulfuric, nitric and hydrochloric acids with hydrogen peroxide and the recovery was above 98% Cu. Yang Zhang et. al (2010) used sulfuric acid and sodium chloride to extract copper, zinc and cobalt from copper smelting slag (1.35% Cu) obtaining a recovery of 98, 97 and 89% respectively. Nadirov R. et. al, using ammonium chloride at 320°C, extracted 91.5, 89.7 and 88.9% of Zn, Cu and Fe respectively, leaching a primary copper smelting slag. In this context, the present work aims to characterize chemically, mineralogically and dangerousness a slag from secondary copper smelting and study the leaching technique to extract the copper. 2. EXPERIMENTAL The slag used in this work was collected from a copper scrap smelter used in the production of copper electrolytic powder. Currently, the waste is stored inside the company, in large "bags" that correspond to different batches of foundry. Samples of different bags were collected, thus reproducing the random characteristics of the process. The flowchart of the steps of this study are shown in Figure 1. First, the samples were comminuted in a hammer mill and a knife mill. For the mineralogical analysis, the manual grinding step, using a mortar and pistil, was also performed. Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 Figure 1 - Flowchart of the experimental stages 2.1 Hazardousness test The hazard assessment of the samples was carried out according to Brazilian Standard ABNT NBR 10.004 which classifies solid waste according to its potential risks to the environment in the following classes: hazardous (Class I) non-inert (Class II-A) and inert (Class II-B). The Brazilian Standard NBR 10.005 described the procedures to obtain the leached extract. The potential toxic elements investigated were: barium (Ba), cadmium (Cd), lead (Pb) and chromium (Cr). The equipment and the configuration of the hazard test are shown in Figure 2. Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 Figure 2- Toxicity test equipment 2.2 Chemical and mineralogical characterization For the chemical analysis, samples with a particle size <2.0 mm were used previously. A 10 g aliquot was leached with 100 ml of nitric (p.a) and hydrochloric acid (p.a) in a ratio of 1: 3 respectively (aqua regia) for 2 hours at 70°C. The solution was filtered and the leached extract was sent for ICP-OES analysis. For the mineralogical analysis a particle size less than 0.074 mm (250 mesh) was used, homogenized and submitted to X-ray diffraction (XRD) analysis. 2.3 Leaching After the characterization of the material, the leaching was started in order to extract the copper. The leaching agent chosen was sulfuric acid (98% w / w H2SO4) isolated or mixed with hydrogen peroxide (3% w / w H2O2) based on previous works cited in the literature about extraction of copper from metallic slag. The leaching was performed using a condenser and magnetic stirrer with heating, as shown in Figure 3. Figure 3- Leaching test configuration. The first tests were performed using only a solution of sulfuric acid at low concentrations (5 - 30%), prepared in a liquid solid ratio of 1:10, for 120 minutes. The parameters tested are shown in Table 1. Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 Table 1 - Parameters used in leaching with diluted H2SO4 Sample Temperature [°C] Concentraation H2SO4 (% v.v.) A1 5 A2 25 15 A3 30 A4 5 A5 70 15 A6 30 After, a concentrated sulfuric acid (p.a.), prepared in a liquid solid ratio of 1: 5, was used. The parameters evaluated are shown in Table 2. Table 2 - Parameters used in leaching with concentrated H2SO4. Sample Temperature[°C] Time [min] L1 120 L2 70 240 L3 360 L4 25 120 L5 240 In sequence, tests were carried out with a solution of sulfuric acid and hydrogen peroxide, prepared in a liquid solid ratio of 1:10 at a temperature of 70°C. The evaluated parameters are shown in Table 3. Table 3 - Parameters used in the leaching with H2SO4 and H2O2. Sample Concentration Concentration Time H2SO4 [%v.v.] H2O2 [% v.v.] [Min] H1/H10 5 1 120/360 H2/H11 15 1 120/360 H3/H12 30 1 120/360 H4/H13 5 2 120/360 Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 H5/H14 15 2 120/360 H6/H15 30 2 120/360 H7/H16 5 5 120/360 H8/H17 15 5 120/360 H9/H18 30 5 120/360 3. RESULTS AND DISCUSSION 3.1 Hazardousness Test The results of the analysis of the extract obtained through NBR 10005 are presented in Table 4. Table 4 - Results of hazardousness analysis Parameter Unit Results MDL A B Barium mg/L 0,102 ND 0.023 Cadmium % ND ND 0.003 Lead mg/L 1,65 1,92 0.042 Chrome mg/L ND ND 0.009 MDL = maximum detection limit - ND = not detected The limits of maximum concentration allowed by the Brazilian standard, to the elements evaluated in the slag, in the extract obtained by the leaching test are presented in table 5. Comparing Tables 4 and 5, it is possible to verified that the lead concentration is above tha the maximum limit of the standard. Since this parameter (lead) the waste (slag) should be classified as: Class I - Hazardous. Table 5 - Limit concentration fixed in standard NBR 10004 Parameter Allowed limit mg/L Barium 70.0 Cadmium 0.5 Lead 1.0 Chrome 5.0 3.2 Chemical and mineralogical characterization The results from the chemical analysis are presented in Table 6. Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 Table 6 - Composition of slag Component Al Ca Cu Fe Pb Si % 0.1 0.21 23 3.1 1.3 1.7 The elements shown in Table 6 are those that are present in greater quantity or which are of interest forrecycling.
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