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Home , Copper extraction, Hydrometallurgy, Slag

CHARACTERIZATION AND RECOVERY OF FROM

A. P. GABRIEL*, L. R. SANTOS*, A.C. KASPER*, H. M. VEIT*

* Materials 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 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 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 (Schlesinger et al., 2011) In addition to primary copper production, there is a significant rate of the copper production from /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 , 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 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 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 or . 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 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 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, and 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 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), (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. It is confirmed that copper is present in large quantities, justifying it as the metal of interest for extraction. From the mineralogical analysis, it is observed that copper is in the form of Cuprita, Covelita and also in the metallic form, besides other present phases, that do not have copper in its composition, as shown in Figure 4.

Figure 4 - X-ray diffraction of the slag

3.3 Leaching

From the three groups of tests performed (sulfuric acid diluted, concentrated and a mixture of sulfuric acid and hydrogen peroxide) only one was efficient, the mixture of hydrogen peroxide and sulfuric acid. The results from this mixture are shown in the Figures 5, 6 and 7. The other tests showed a recovery rate less than 10%, indicating that the majority of copper is in the metallic form and thus, requiring the action of an oxidative agent stronger. The irregular behavior of the rates, as a function of the leaching time and as a function of the H2SO4 / H2O2 ratio, demonstrates the need for further testing. A possible explanation for this irregular behavior is the large heterogeneity of the samples that may have great influence on the results.

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

Figure 5 - Extraction of Cu to 5% v.v. of H2SO4 Figure 6 - Extraction of Cu to 15% v.v. of H2SO4

Figure 7 - Extraction of Cu to 30% v.v. of H2SO4

4. CONCLUSION

The evaluated material (slag) constitutes a hazardous waste, Class I according to the criteria of Brazilian Standard (NBR 10.004). So, a correct disposal requires specific procedures with high economic costs involved. According to chemical characterization, the slag has an extremely high copper content compared to primary copper slag and to ores from which copper is currently extracted. The copper in the slag is in the form of Cuprita, Covelita and also in the metallic form. In this way, the development of a recovery route is very attractive due to the benefits to the environment and economic. A metallurgical route using , through leaching, proved to be feasible for the extraction of copper and the main factors to be controlled are the concentration of sulfuric acid and hydrogen peroxide, time and temperature leaching and homogeneity of the samples. The best result, from leaching test, was obtained for a sample of 10 g of slag in a 100 ml of extraction solution containing 5% vv of H2SO4 and 1% vv of H2O2. With this configuration was possible to extract 72% of Cu present in the slag.

REFERENCES

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Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

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