Reduction of Chilean copper slags: a case of waste management project

Pressure Leaching of Copper Slag Flotation Tailings in Oxygenated Sulfuric Acid Media

In this study, a hydrometallurgical method for the recovery of copper, cobalt, and zinc from copper slag flotation tailings (SFT) was investigated. SFT contains large amounts of valuable metallic compounds, such as copper, cobalt, and zinc. A representative SFT sample containing 0.50% Cu, 0.148% Co, 3.93% Zn, and 39.50% Fe was used in experimental studies. High-pressure oxidative acid leaching of SFT was carried out to assess the effects of sulfuric acid concentration, oxygen partial pressure, reaction time, solid/liquid ratio, and temperature on the extraction of copper, cobalt, zinc, and iron. The dissolution of metals from the SFT sample increased with temperature and sulfuric acid concentration. However, high acid concentrations and high solid/liquid (S/L) ratios led to gel formation that caused filtration problems and inhibited metal dissolution. The optimum leaching conditions were found to be a leaching time of 90 min, an acid concentration of 250 kg/t, a temperature of 220 °C, an S/L ratio of 1:5, and an oxygen partial pressure of 0.7 MPa. Under these conditions, 93.1 ± 1.1% Cu, 96.3 ± 1.8% Co, and 92.3 ± 1.7% Zn were extracted. Iron dissolution was only 0.5 ± 0.1%. This hydrometallurgical process almost completely recovers valuable metals. In particular, cobalt, which is of great importance in the production of lithium-ion batteries, has been declared a critical metal by the United States, Canada, and the EU and was taken into solution with very high extraction efficiency (>95%). Additionally, oxygen partial pressure enhanced copper, cobalt, and zinc dissolution. When O2 was not introduced into the leaching system, the extraction efficiencies of Co, Cu, and Zn were approximately 24.5, 5.3, and 26.3%, respectively, after 2 h of leaching treatment.

Chemical Composition Data of the Main Stages of Copper Production from Sulfide Minerals in Chile: A Review to Assist Circular Economy Studies

The mining industry has faced significant challenges to maintaining copper production technically, economically, and environmentally viable. Some of the major limitations that must be overcome in the coming years are the copper ore grade decline due to its intense exploitation, the increasing requirements for environmental protection, and the need to expand and construct new tailings dams. Furthermore, the risk of a supply crisis of critical metals, such as antimony and bismuth, has prompted efforts to increase their extraction from secondary resources in copper production. Therefore, improving conventional processes and developing new technologies is crucial to satisfying the world’s metal demands, while respecting the policies of environmental organizations. Hence, it is essential that the chemical composition of each copper production stage is known for conducting these studies, which may be challenging due to the huge variability of concentration data concerning the ore extraction region, the process type, and the operational conditions. This paper presents a review of chemical composition data of the main stages of copper production from sulfide minerals, such as (1) copper minerals, (2) flotation tailings, (3) flotation concentrates, (4) slags and (5) flue dust from the smelting/converting stage, (6) copper anodes, (7) anode slimes, (8) contaminated electrolytes from the electrorefining stage, (9) electrolytes cleaned by ion-exchange resins, and (10) elution solutions from the resins. In addition, the main contributions of recent works on copper production are summarized herein. This study is focused on production sites from Chile since it is responsible for almost one-third of the world’s copper production.

Environmental and Socioeconomic Impact of Copper Slag—A Review

Copper slag is generated when copper and nickel ores are recovered from their parent ores using a pyrometallurgical process, and these ores usually contain other elements which include iron, cobalt, silica, and alumina. Slag is a major problem in the metallurgical industries as it is dumped into heaps which have accumulated into millions of tons over the years. Moreover, they pose a danger to the environment as they occupy vacant land (space problems). Over the past few years, studies have been conducted to investigate the copper slag-producing outlets to learn their behavior, as well as properties of slag, to have the knowledge of how to better reuse and recycle copper slag. This review article provides the environmental and socioeconomic impacts of slag, as well as a characterization of copper slag, with the aim of reusing and recycling the slag to benefit the environment and economy. Recycling methods are considered an attractive technological pathway for reducing waste and greenhouse gas emissions, as well as promoting the concept of circular economy through the utilization of waste. These metal elements have value depending on their characteristics; hence, copper slag is considered as a secondary source of valuable metals. Some of the pyrometallurgical and hydrometallurgical processes to consider are physical separation, magnetic separation, flotation, leaching, and direct reduction roasting of iron (DRI). Some of the possible metals that can be recovered from the copper slag include Cu, Fe, Ni, Co, and Ag (precious metals).

A potential industrial waste-waste co-treatment process of utilizing waste SO2 gas and residue heat to recover Co, Ni, and Cu from copper smelting slag

A potential industrial waste-waste co-treatment process was proposed and verified for the recovery of the valuable metals Co, Ni, and Cu from copper smelting slag by utilizing high temperature SO₂ off-gas. Sulfation roasting followed by water leaching under designed thermodynamic conditions was conducted to facilitate the selective formation of Co, Ni, and Cu sulfates while separating iron as oxide. Several parameters were studied such as roasting temperature, roasting time, the addition of Na₂SO₄, and leaching agent. Under the optimized sulfation roasting conditions (Gas flow: 500 mL/min, 5% SO₂ +20% O₂ +75% Ar; Roasting temperature: 650 °C; Roasting time: 4 h; Addition of Na₂SO₄: 30%) followed by water leaching (Leaching temperature: 80 °C; Leaching time: 5 h; solid to liquid ratio: 0.05 g/mL), the extraction yields of Ni, Co, and Cu were shown to reach 95.8% and 91.8%, 81.6%, respectively. Furthermore, the sulfation roasting - water leaching process was confirmed on lab-scale as a feasible and efficient way to recover valuable metals and the mechanism was determined and verified from the microstructural evolution. Finally, a potential environmentally friendly industrial process in terms of the energy flow and material flow was presented based on preliminary assessments for environmental benefits, economic benefits, and heat recovery.

Value-added strategies for the sustainable handling, disposal, or value-added use of copper smelter and refinery wastes

Metallurgical plants constituting of smelters and refineries recover metals (i.e., copper) from mineral deposits. Copper production generates several waste streams of which slag, sludge and dust are generated in the largest quantities. The need to eliminate or at least reduce their adverse effects on the environment call for developing methods for recovering valuable components such as copper, zinc and iron through their selective separation from toxic components present in the waste (mainly arsenic and lead). This can be achieved through hydrometallurgical methods (leaching with organic and inorganic media), techniques facilitating mobility of elements (roasting with leaching) and biological processes (bioleaching). The valorization of metallurgical waste as a source of fertilizer micronutrients can be a sustainable and value-added direction of its management. This review presents ways of useful-metals recovery from the copper smelter and refinery wastes, including selective separation of valuable metals. The novelty of this review is a demonstration of the application potential of recovered components from metallurgical waste in the agricultural sector.

Battery Scrap and Biochar Utilization for Improved Metal Recoveries in Nickel Slag Cleaning Conditions

Cobalt is a critical, high-value metal used extensively in batteries and other sustainable technologies. To secure its supply in future, it is utmost important to recover cobalt efficiently from industrial wastes and recycled End-of-Life batteries. This study aims at finding ways to improve the reduction of cobalt as well as valuable metals nickel and copper in nickel slag cleaning furnace conditions by using both traditional fossil-based coke and a more sustainable option, low-CO2 footprint biochar, as reductants. A cobalt-rich fraction of battery scrap (25.5 wt% Co) was also used as a secondary feed. The experimental technique consisted of reduction experiments with different times at 1400 °C under inert atmosphere, quick quenching and Electron Probe X-ray Microanalysis. The use of biochar resulted in faster reaction kinetics in the reduction process, compared to coke. Moreover, the presence of battery scrap had a clear impact on the behavior and reduction kinetics of the elements and/or enhanced settling and separation of matte and slag. The addition of scrap increased notably the distribution coefficients of the valuable metals but consequently also the iron concentration in matte which is the thermodynamic constraint of the slag cleaning process.

Statistical Study for Leaching of Covellite in a Chloride Media

Covellite is a secondary copper sulfide, and it is not abundant. There are few investigations on this mineral in spite of it being formed during the leaching of chalcocite or digenite; the other investigations on covellite are with the use of mineraloids, copper concentrates, and synthetic covellite. The present investigation applied the surface optimization methodology using a central composite face design to evaluate the effect of leaching time, chloride concentration, and sulfuric acid concentration on the level of copper extraction from covellite (84.3% of purity). Copper is dissolved from a sample of pure covellite without the application of temperature or pressure; the importance of its purity is that the behavior of the parameters is analyzed, isolating the impurities that affect leaching. The chloride came from NaCl, and it was effectuated in a size range from –150 to +106 μm. An ANOVA indicated that the leaching time and chloride concentration have the most significant influence, while the copper extraction was independent of sulfuric acid concentration. The experimental data were described by a highly representative quadratic model obtained by linear regression (R2 = 0.99).

Perspectives regarding the use of metallurgical slags as secondary metal resources - A review of bioleaching approaches

Smelting activity by its very nature produces large amounts of metal-bearing waste, often called metallurgical slag(s). In the past, industry used to dispose of these waste products at dumping sites without the appropriate environmental oversight. Once there, ongoing biogeochemical processes affect the stability of the slags and cause the release of metallic contaminants. Rather than viewing metallurgical slags as waste, however, such deposits should be viewed as secondary metal resources. Metal bioleaching is a "green" treatment route for metallurgical slags, currently being studied under laboratory conditions. Metal-laden leachates obtained at the bioleaching stage have to be subjected to further recovery operations in order to obtain metal(s) of interest to achieve the highest levels of purity possible. This perspective paper considers the feasibility of the reuse of base-metal slags as secondary metal resources. Special focus is given to current laboratory bioleaching approaches and associated processing obstacles. Further directions of research for development of more efficient methods for waste slag treatment are also highlighted. The optimized procedure for slag treatment is defined as the result of this review and should include following steps: i) slag characterization (chemical and phase composition and buffering capacity) following the choice of initial pH, ii) the choice of particle size, iii) the choice of the liquid-to-solid ratio, iv) the choice of microorganisms, v) the choice of optimal nutrient supply (growth medium composition). An optimal combination of all these parameters will lead to efficient extraction and generation of metal-free solid residue.

Recovery of metal values from copper slag and reuse of residual secondary slag

Resource and environmental factors have become major forces in mining and metallurgy sectors driving research for sustainability purposes. The concept of zero-waste processing has been gaining ground readily. The scant availability of high quality raw materials has forced the researchers to shift their focus to recycling while the exceedingly stringent environmental regulations have forced researchers to explore new frontiers of minimizing/eliminating waste generation. The present work is aimed at addressing both aspects by employing recycling to generate wealth from copper slag and producing utilizable materials at the same time thus restoring the ecosystem. Copper slag was characterized and processed. The pyro-metallurgical processing prospects to generate utilizable materials were arrived at through rigorous thermodynamic analysis. Carbothermal reduction at elevated temperature (near 1440°C) helped recover a majority of the metal values (e.g., Fe, Cu and Mo) into the iron-rich alloy product which can be a feed material for steel making. On the other hand, the non-metallic residue, the secondary slag, can be used in the glass and ceramic industries. Reduction time and temperature and carbon content were shown to be the most important process variables for the reaction which were optimized to identify the most favored operating regime that maximizes the metal recovery and simultaneously maximizes the hardness of the secondary slag and minimizes its density, the two major criteria for the secondary slag product to be utilizable. The flux addition level was shown to have relatively less impact on the process performance if these are maintained at an adequate level. The work established that the copper slag, a waste material, can be successfully processed to generate reusable products through pyrometallurgical processing.

Urinary Metal Levels in a Chilean Community 31 Years After the Dumping of Mine Tailings

BACKGROUND

Between 1938 and 1975, the city of Chañaral, located in the north of Chile, received 200 megatons of unregulated mining waste, which created an artificial beach 10 kilometers long and covering an area larger than 4 km2. In 1983, this deposit was classified as a serious case of marine pollution in the Pacific Ocean, according to the Organization for Economic Cooperation and Development. In 1989, dumping ceased due to a judicial order. Until now, the effects of this pollution on the population living around these mine tailings has been unknown.

OBJECTIVE

To determine the prevalence of exposure to metals by dust from mine tailings in Chañaral, a city located in the northern mining area of Chile.

METHODS

The level of urinary metals in a representative sample of adults from Chanaral was determined.

RESULTS

Urinary levels of total arsenic (44.6 μg/L), inorganic arsenic (17.0 μg/L) and nickel (2.8 μg/L) were higher than in other areas of Chile. Levels of copper (17.9 μg/L), mercury (1.6 μg/L) and lead (0.9 μg/L) exceeded international values. Of the total subjects, 67.5%, 30.4%, 29.4%, 16.9%, 13.2 and 9.3% presented with high levels of copper, nickel, total arsenic, inorganic arsenic, mercury and lead, respectively.

CONCLUSION

Thirty-one years after suspension of the discharge of mining waste, the local population in this area remains exposed to metals from the mine tailings. Surveillance and remedial actions addressing the Chañaral mine tailings are needed.

Study on the Reduction of Ferrous Compounds Disseminated in Fayalite, Vitreous and Magnetite in Dumped Copper Slag by Means of Carbonthermic Method

Carbonthermic method was adopted to reduce the iron in the form of fayalite in copper slag to metal iron in this study. The reduction was undertaken under the conditions of roasting reduction at 1423 K for 4 h with specified parameters that the ratio of copper slag versus anthracite was 2∶1, and that the ratio of calcium carbonate to silicon dioxide was 1.43∶1. It was demonstrated that the metallization efficiency of iron could reach 88.26%. Moreover it was showed that the reduction process of fayalite by carbon could be routed as: Fe2SiO4(or 2FeO·SiO2)→ FeO + 2CaO·SiO2→ Fe. In addition it was proved that the combination ability between calcium positive ion and silicon oxygen anion was bigger than that between iron positive ion and silicon oxygen anion. As a result，SiO2 compacted in fayalite could decompose easily and could combine with CaO at the reaction temperature, therefore FeO could exist with a form of freedom state which could be reduce easily by carbon or monocarbon produced in carbonthermic method.

Thermal decomposition of pyrometallurgical copper slag by oxidation in synthetic air

The purpose of this study was to investigate the possibility of separating pyrometallurgical copper (fayalite) slag by oxidation in a synthetic air atmosphere into ferrous and silicate phases suitable for resources to be recovered from them. Isothermal oxidation kinetics and the most probable reaction models are studied in the temperature range of 773 to 1173 K using thermogravimetric analysis data and the classical Johnson-Mehl-Avrami-Yerofeev-Kolmogorov (JMAYK) equation. Depending on the model applied, the activation energies of fayalite slag oxidation in the temperature range of 773-973 K were: D1: 37.55 kJ mol(-1); D2: 43.27 kJ mol(-1); D3: 50.52 kJ mol(-1); and D4: 45.65 kJ mol(-1). Depending on the model applied, the activation energies of fayalite slag oxidation in the temperature range of 1073-1173 K were: F1: 20.48 kJ mol(-1); R2: 20.45 kJ mol(-1); R3: 20.18 kJ mol(-1); A2: 21.54 kJ mol( -1) and A3: 22.34 kJ mol(-1). The transformation of fayalite to hematite and amorphous silica was completed after 1435, 1350 and 1080 s at temperatures of 1073, 1123 and 1173 K, respectively. The following oxidation products were identified by X-ray diffraction: (1) fayalite, hematite and magnesioferrite (Fe(2)MgO(4)) in the temperature range 773 to 973 K; and (2) hematite and magnesium iron oxide (Mg(1.55)Fe( 1.6)O(4)) in the temperature range of 1073 to 1173 K.

Immobilization of copper flotation waste using red mud and clinoptilolite

The flash smelting process has been used in the copper industry for a number of years and has replaced most of the reverberatory applications, known as conventional copper smelting processes. Copper smelters produce large amounts of copper slag or copper flotation waste and the dumping of these quantities of copper slag causes economic, environmental and space problems. The aim of this study was to perform a laboratory investigation to assess the feasibility of immobilizing the heavy metals contained in copper flotation waste. For this purpose, samples of copper flotation waste were immobilized with relatively small proportions of red mud and large proportions of clinoptilolite. The results of laboratory leaching demonstrate that addition of red mud and clinoptilolite to the copper flotation waste drastically reduced the heavy metal content in the effluent and the red mud performed better than clinoptilolite. This study also compared the leaching behaviour of metals in copper flotation waste by short-time extraction tests such as the toxicity characteristic leaching procedure (TCLP), deionized water (DI) and field leach test (FLT). The results of leach tests showed that the results of the FLT and DI methods were close and generally lower than those of the TCLP methods.

Treatment of copper industry waste and production of sintered glass-ceramic

Copper waste is iron-rich hazardous waste containing heavy metals such as Cu, Zn, Co, Pb. The results of leaching tests show that the concentration of these elements exceeds the Turkish and EPA regulatory limits. Consequently, this waste cannot be disposed of in its present form and therefore requires treatment to stabilize it or make it inert prior to disposal. Vitrification was selected as the technology for the treatment of the toxic waste under investigation. During the vitrification process significant amounts of the toxic organic and inorganic chemical compounds could be destroyed, and at the same time, the metal species are immobilized as they become an integral part of the glass matrix. The copper flotation waste samples used in this research were obtained from the Black Sea Copper Works of Samsun, Turkey. The samples were vitrified after being mixed with other inorganic waste and materials. The copper flotation waste and their glass-ceramic products were characterized by X-ray analysis (XRD), scanning electron microscopy and by the toxicity characteristic leaching procedure test. The products showed very good chemical durability. The glass-ceramics fabricated at 850 degrees C/2 h have a large application potential especially as construction and building materials.