Treatment of copper-containing leaching residue by sulfation roasting followed by acid/water leaching

15 This research investigates the extraction of copper from copper-containing leaching residue, which includes 33.45% of copper, 14.14% of iron, 23.87% of sulfur and trace amounts of silver and other elements. Roasting the copper-containing residue under air and oxygen flow convert 18 sulfides into sulfate, followed by water and acid leaching to extract copper. The process parameters, including leaching temperature, sulfuric acid concentration, leaching time, solid-to-liquid ratio, and agitation speed, were optimized for both water and acid leaching methods. 21 Results showed that the maximum copper dissolution efficiency was 93.12% with water leaching, and 97.16% with acid leaching. Chemical analysis revealed that the water and acid leaching residue contained 48.13% and 31.64% of iron, respectively. This study provides

Results showed that the maximum copper dissolution efficiency was 93.12% with water leaching, and 97.16% with acid leaching. Chemical analysis revealed that the water and acid leaching residue contained 48.13% and 31.64% of iron, respectively. This study provides 24 valuable insights into the process optimization for copper extraction from copper-containing leaching residue, which can inform the development of more efficient and sustainable methods for metal recovery. Keywords: copper technogen concentrate, thermal analysis, air-and oxygen roasting, acid/water leaching m a n u s c r i p t

INTRODUCTION
The growing demand for copper has resulted in the depletion of copper ores with higher copper content, leading to the treatment of complex polysulfides or copper ore with higher contents of 33 impurities such as Sb, Pb, Zn, As, Hg, Ni etc. Among these impurities, arsenic is particularly challenging due to its toxicity. There are several significant polymetallic ore deposits in Mongolia including Tsav, Boorchi, Tolbo, Kharmagtai and Asgat. In recent years, there has been interest 36 in developing the Asgat deposit as well as other mineral deposits in the country, to meet the growing demand for metals and minerals worldwide. Asgat polymetallic deposit is estimated to hold approximately 6402.6 thousand of tonnes of ore, boasting a valuable metal reserve 39 including 2247.8 tonnes of silver, 7264.6 tonnes of copper, 31830.9 tonnes of antimony and 3319.8 tonnes of bismuth. Although Asgat is primarly known for its polymetallic ore composition, it can also be regarded as a potential source of copper due to the significant presence of 42 tetrahedrite, which constitutes 72% of the Asgat concentrate [1][2][3].
Processing of polymetallic concentrates is difficult task as it involves a variety of minerals such as enargite (Cu3AsS4), tennantite (Cu12As4S13) and tetrahedrite (Cu12Sb4S13) associated with 45 other sulfide minerals [4]. To separate the target metals from the polymetallic ore concentrate, scientists have focused on removing harmful impurities. Comprehensive study on thermal and kinetic study of polymetallic copper concentrate was conducted by Mitovski et. al [5].

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Tetrahedrite represents the main chemical source of copper (40-46%) and antimony (27-29%) along with other important elements including arsenic, bismuth, mercury, and silver. Two main leaching methods for tetrahedrite have been identified-alkaline and acidic leaching [6]. Balaz 51 et.al studied leaching of mercury and antimony from tetrahedrites of different characteristics using an alkaline solution [7] while the leaching of tetrahedrite using HCI in the presence of ozone was studied by Ukasik et. al [8].

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The leaching residue can be further processed through an appropriate roasting process to convert the metals into extractable form by heating at high temperature [9][10][11]. Three types of roasting methods are commonly used including oxidation roasting, chlorination roasting, and 57 sulfation roasting [12]. However, oxidation roasting requires high temperatures and may lead to copper loss as copper ferrite. Chlorination roasting tends to generate toxic and corrosive oxychlorides [13]. On the other hand, sulfation roasting has been found to be quite suitable for 60 subsequent processing. Nevertheless, during sulfation roasting, the reaction becomes complex when more than one sulfide is present in the sample.
Roasting is a surface reaction that results in the formation of an oxide layer. This layer remains 63 porous allowing oxygen to pass into the unreacted inner sulfide portion of the particle, while the resulting SO2 gas is released [14]. The sulfuric gas then reacts with metal oxides and excess A c c e p t e d m a n u s c r i p t oxygen to form sulfates, making the sulfation roasting process an environmentally friendly 66 technology. To produce a mixed oxide-sulfate product sulfation roast is preferred, making it an ideal process for polysulfide compound. While there have been numerous investigations conducted, our study provides a comprehensive analysis of copper extraction from copper 69 technogen concentrate sourced from domestic ore deposits.
This study aimed to assess the effectiveness of extracting copper from copper-containing leaching residue of polysulfide concentrate. The process involved sulfation roasting followed by 72 leaching with water and sulfuric acid. To determine the optimal conditions for sulfation roasting, the study examined the effects of roasting temperature and time under an air and oxygen atmosphere. After roasting, the resulting product was leached using water and sulfuric acid to 75 obtain a copper-bearing aqueous solution. Copper sulfate was the predominant compound in the solution.

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Materials: The raw material used in this study was the polysulfide concentrate obtained from the Asgat mining ore in Mongolia. The concentrate was initially subjected to alkaline-sulfide leaching (using NaOH/Na2S x 9H2O) to obtain a technogen concentrate also named copper containing 81 leaching residue, containing 33.45% copper, which was subsequently utilized for copper extraction.
TG/DTA analysis: Thermal analysis of the copper technogen concentrate was carried out using

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After completion of the leaching process, the slurry was filtered and the leaching residue was washed continuously with distilled water and dried in an oven. The leachates and leach residue were analyzed using ICP-OES, XRD, SEM and chemical analysis to determine the constituents.

RESULTS AND DISCUSSION
Asgat polymetallic ore concentrate is composed of several metals, including 0.91% silver, 18.2% copper, 19.4% antimony, 2.03% arsenic, and 1.6% bismuth, as well as other elements. In order 108 to remove toxic contaminants such as antimony, arsenic, and bismuth, the concentrate was subjected to alkaline-sulfide leaching. The activation energy for antimony leaching from the tetrahedrite by alkaline-sulfide leaching was calculated as 81.43 kJ/mol which indicates the 111 leaching is controlled by surface chemical reaction [15]. These findings are consistent with those of other researchers [16].
The elemental composition of Asgat concentrate and leaching residue are compared in Table 1 114 [15]. The alkaline-sulfide leaching residue contains 33.45% of copper, 14.14% of iron, 23.87% of sulfur, 0.73% of silver and other trace elements such as silicon, aluminium and sodium.
According to the XRD analysis, the leaching residue contains chalcopyrite (CuFeS2), covellite 117 (CuS), chalcocite (Cu2S), pyrite (FeS) and argentite (Ag2S) as well as non-ore sulfide minerals as shown in Fig. 1 and Table 2.        Roasting under air: The purpose of the roasting stage was to convert copper sulfide into easily 159 soluble copper sulfate. In comparison to conventional roasting processes, we have an advantage in using lower roasting temperature and eliminating the need for added sulfuric acid [9] or sodium sulfite as sulfation agent [12]. To achieve this, the copper-containing leaching 162 residue was underwent roasting in a Nabertherm tube furnace under an air atmosphere at varying temperatures, ranging from 400 to 600 o C as determined by TG/DTA analysis. Roasting times varied from 15 minutes to 3 hours.

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In this study, we examined the weight increase during sulfation roasting under varying times and temperatures. The results showed that the highest weight increase of 32.21% is occurred at 550 o C for one hour of roasting time under air atmosphere as shown in Fig. 3. Additionally, the color 168 difference of the roasted products can indicate whether sulfation roasting is complete. Lighter A c c e p t e d m a n u s c r i p t colors were observed at lower temperatures or shorter roasting times, whereas completed roasting resulted in darker colors due to copper sulfation.

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The chemical composition of the roasted product is confirmed through an XRD study (refer Fig.   4) revealing that 67.8% of the product was comprised of copper sulfate, while 27.2% composed goethite and 4.8% albite. This finding indicates that almost 95% of copper was successfully 174 converted to copper sulfate during the roasting process. The oxidation of chalcopyrite, covellite and chalcocite during roasting was responsible for this conversion [17]. Furthermore, iron compounds were also present in the roasted product in addition to copper sulfate.

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Roasting under oxygen: The copper-containing residue was subjected to roasting under varying conditions of temperature, time, and oxygen flow rate. The results of the study, depicted in Fig.   3, showed that the maximum weight gain for air roasting was 32.21% at one hour of roasting 180 time, while oxygen roasting produced a maximum weight gain of 29.85%. However, when the roasting time was increased to three hours, the maximum weight gain for oxygen roasting was found to be 33.15%. X-ray diffraction (XRD) data indicated that with roasting times less than 183 three hours at temperature less than 400 o C for oxygen roasting, FeS2 and CuS still existed, suggesting that the sulfation roasting was not complete. At three hours of roasting time, copper sulfates dominated, along with other minerals such as magnetite (Fe3O4), goethite FeO(OH), 186 and iron sulfates Fe2(SO4)3. Therefore, the optimum conditions for oxygen roasting were determined to be a roasting temperature of 400 o C, a roasting time of 3 hours, and an oxygen flow rate of 20 ml/min (refer Table 3). XRD analysis of the roasted sample revealed a 189 composition of 64.8% copper sulfate, 3.6% goethite, 4.5% hematite, 3.5% magnetite, and 18.7% albite with approximately 12% iron compounds present in the roasted product.  Composition of our sample, which includes metal sulfides such as chalcopyrite (CuFeS2), composition during sulfation roasting. However, other process parameters such as particle size, mixing, reaction time and roasting technique can also significantly impact the final product [18].
The sulfation roasting process is complete at 550 o C during the air roasting, but, when oxygen 204 roasting is used, a lower temperature of 400 o C is required for the sulfation process.
Leaching test with water: The copper technogen concentrate was roasted under optimum conditions and subsequently leached using water at various temperature to obtain a copper-

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A c c e p t e d m a n u s c r i p t bearing aqueous solution. The water leaching experiments were conducted by varying the leaching time, temperature, agitating speed and solid-to-liquid ratio.
The dissolution efficiency (%), which is a measure of how much of the total copper is dissolved, 210 was calculated using the equation given below: The copper dissolution efficiency was found to be at its highest with a rate of 91.  The agitation speed is an another important parameter in leaching experiments, and its effect on copper and iron dissolution was studied within the range of 200-500 rpm. For the air roasted 225 sample, the copper dissolution rate decreased slowly until 400 rpm but, increased to 91.68% at 500 rpm. The copper dissolution rate for the oxygen roasted sample increased gradually with the increase of agitation speed and reached a maximum value of 93.12% at 400 rpm. Iron 228 dissolution was generally low for the air roasted sample, whereas for the oxygen roasted sample, high iron dissolution was observed, especially at 300 rpm (refer to Fig. 6). This can be attributed to the increased molecular motion of iron sulfate as agitation speed increased, leading to a 231 corresponding increase in iron dissolution.
The copper and iron dissolution rates were also studied as a function of solid-to-liquid ratio, as shown in Fig. 7. For both air and oxygen roasted sample, the optimum solid-to-liquid phase ratio 234 was found to be 1:50 with copper dissolution rates of 91.68% and 93.12%, respectively. We assume that water-insoluble compounds were also present in the roasted sample. At the 1:50 phase ratio, the iron dissolution rate was low, at 16.49% indicating that most of the iron   However, the dissolution of iron is highest with lower solid-to-liquid ratio, particularly for the 267 oxygen roasted sample. Fig. 11 illustrates the impact of agitation speed on copper dissolution. In the case of the air roasted sample, 200 rpm was determined to be the optimal agitation speed as it resulted in 270 97.16% copper dissolution. However, the iron dissolution rate was found to be relatively high.
For the oxygen roasted sample, the highest copper dissolution rate (99.59%) was achieved at 300 rpm, with a lower amount of iron dissolved in the leachate.

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Leaching processes of copper compounds in the water and sulfuric acid proceeds via diffusion and activation energy were calculated as 6.05 and 8.70 kJ/mol.  Fig.13a).

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A c c e p t e d m a n u s c r i p t This residue could be utilized as an iron resource and further processed to recover iron, thereby ensuring complete utilization of the raw material without generating any waste.
The morphology of the leaching residue after the water and acid leaching both for air (a,b) and 294 oxygen (c,d) roasted samples were shown in Fig. 13. SEM-EDS analysis confirmed the intensity of energy peaks corresponding to Fe, O2 and Si with about 44% of Fe content. Copper bearing aqueous solution: The resulting leach liquor after the water/acid leaching will be 309 further utilized to produce a high-purity electrolyte with a high concentration of Cu through solvent extraction. This electrolyte will then be used to electroplate a pure cathode copper. Our study suggests a shorter flowsheet of extracting the copper from the polysulfide concentrate, 312 which includes a leaching process to remove the impurities such as arsenic, sulfation roasting, water/acid leaching and subsequent solvent extraction.

CONCLUSIONS
We systematically optimized the leaching processes for extracting copper from air and oxygen roasted samples using both water and sulfuric acid leaching methods. The parameters for water Our results indicated that acid leaching yielded a higher copper dissolution efficiency compared to water leaching, with values of 97.16% and 91.68%, respectively, for air roasted sample.

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Similarly, for the oxygen roasted sample, acid leaching achieved a copper dissolution efficiency of 95.53%, while water leaching resulted in 93.12%. Notably, both methods exhibited a certain degree of iron dissolution efficiency, with approximately 15% and 30% present in the leachate 327 for the air roasted and oxygen roasted samples, respectively.
XRD analysis confirmed the presence of hematite, goethite, magnetite and albite in the hard residue. After water and acid leaching, the hard residue contained 48.13% and 31.64%, total 330 iron, respectively. This indicates that water leaching was more effective in separating the iron compound, resulting in a higher concentration of iron in the hard residue. In conclusion, our c d A c c e p t e d m a n u s c r i p t