The pH-dependent leaching behavior of slags from various stages of a copper smelting process: Environmental implications (original) (raw)
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Legacy base metal slags can generate toxic leachates
Powder Diffraction, 2017
Slags sourced from a derelict zinc–lead–copper–silver–tungsten mine were examined for their bulk elemental composition and mineralogy. pH, oxidation–reduction potential, and the leachability of selected elements (sulphur, calcium, iron, copper, zinc, and lead) were assessed during a 130-day deionised water extraction conducted under oxic conditions. Slags were rich in silicon, iron, copper, zinc, and lead, hosted within minerals including quartz (SiO2), goethite [FeO(OH)], augite [Ca(Mg,AI,Fe)Si2O6], and lead (Pb0). Leachates from the slags increased in analyte concentration throughout the 130-day experiment, with iron, copper, zinc, and lead attaining >5 mg l−1 in some samples. These findings indicate that this pyrometallurgical waste should not be considered environmentally inert, as leachates emanating from them in the field might pose a significant risk to the environment.
Copper Metallurgical Slags – Current Knowledge And Fate: A Review
Critical Reviews in Environmental Science and Technology, 2015
Cu-slags are a by-product of pyrometallurgical processing and contain elevated concentrations of metallic elements that may be released during weathering. Hence, they may pose environmental risk and thus need to be properly disposed off. On the other hand, the high residual content of metals makes slags interesting as secondary resources for metal recovery. This review presents current knowledge about the chemical and phase composition of Cu-metallurgical slags and discusses environmental issues related to their disposal. Furthermore, it provides an overview of experimental approaches assessing environmental risk as well as recent achievements regarding the leaching and recovery of valuable metals from Cu-slags.
LEACHING OF HEAVY METALS FROM THE STEEL SLAG UNDER VARIABLE CONDITIONS
Leaching of metals from steel slag in a systematic manner would lead to the recovery of the metals. Leaching studies are performed on the steel slag under the acidic, neutral and alkaline conditions. Effect of different conditions on the leaching of heavy metals such as Bi, Pd, Cr, Cu, Ni, Zn, As and Fe are analyzed from the steel slag set for the period for 7 days, 30 days and 50 days. The L/S ratio of 10 is used for all the studies. The leaching pattern has been discussed.The study on the steel slag shows that metals such as Cr, Fe, Ni, Zn and Pd leach out more under acidic conditions whereas metals such as Bi, Cu and As leach out more under alkaline conditions. Apart from As most of the metals were found to be leaching within the permissible limits. It is also found that the returns on the metal recovery is very less and is found to be very uneconomical.
Copper slags are usually considered a waste and characterized only by the final copper content. Large and increasing quantities are being produced and disposed of by stockpiling near the metallurgical plants. This paper stresses the importance of physico-chemical characterization when considering uses for slags and the possibility of recovering the valuable metals still remaining in this phase. The purpose of this work is to support and encourage a change in the classical perception of slag from a 'waste' to a 'resource'; promote the development of new technologies for treatment to recover residual values and encourage a search for new uses; with the ultimate objective of eliminating slag stockpiles thereby diminishing the environmental impact of smelting operations. Some of the results of experimental laboratory work done by the authors and examples of commercial applications will be shown. A promising future for valorization and utilization of slags is expected and will provide an example when considering the use of all the other large quantities of wastes generated by the mining industry.
Base metals recovery from copper smelter slag by oxidising leaching and solvent extraction
Hydrometallurgy, 2002
Due to its amorphous structure, smelter slag cannot efficiently be leached with sulphuric acid; the formation of silica gel induces an increase of leach liquor viscosity, difficult pulp filtration and crud formation during solvent extraction. The problem was solved by leaching with sulphuric acid under hydrogen peroxide, which also performs simultaneous iron oxidation and removal.A copper smelter slag from Lubumbashi, Democratic Republic of Congo, containing 1.4% Cu, 0.7% Co, 8.9% Zn and 20.9% Fe(II), has been used in this study. The leaching tests have been carried out at normal pressure on ground slag samples (<100 μm). Silica gel-free solutions containing copper, cobalt and zinc were produced, so that pulp filtration could be easily carried out.The dissolved base metals were successfully extracted from solution by solvent extraction using kerosene Shellsol D70 as diluent. Copper was extracted with LIX 984 and stripped with sulphuric acid solution. Thereafter, cobalt and zinc were collectively extracted with D2EHPA and then separated by selective scrubbing with sulphuric acid solutions of different dilutions. This method provided an overall recovery of 80% Cu, 90% Co and 90% Zn in separated solutions which could be further treated by electrowinning or salt precipitation.
Research on the Recovery of Copper from Metallurgical Slag
Mining Revue, 2021
Metallurgical slag is one of the most common industrial wastes. Many of these wastes are not stable over time, by reacting with water and air, continuously generating emissions of heavy metals. Metallurgical slag processing is necessary for at least two reasons: reducing pollutant emissions and broadening the raw material base. The recovery of these slags is very difficult because they are the result of metallurgical processes that aimed to fix metals considered impurities in chemical matrices as stable as possible. This paper presents the initial research on the behavior of metallurgical slags against different leaching technologies.
Bioleaching and recovery of metals from final slag waste of the copper smelting industry
Minerals Engineering, 2011
Solid waste from the copper smelting industry may be harmful if disposed of in the environment, but it may be a valuable resource if metals can be recovered. The purpose of this study was to evaluate the acid bioleaching of metals from a sample of final smelter slag and the recovery of metals from the leach liquors. Bioleaching was tested in a continuously stirred tank reactor (CSTR) at 20-25°C with 5% pulp density (particle size 75% <47 lm). The yields of metal solubilization after 29 days of contact were 41% Fe, 62% Cu, 35% Zn and 44% Ni. Metals were precipitated in a separate CSTR by titrating the leach liquors with sulfide-rich effluent from a sulfate-reducing fluidized-bed reactor (FBR) (25°C) to desired pH values. Over 98% of the Cu precipitated at pH P 2.8 and over 99% of the Zn precipitated at pH P 3.9. The precipitation of Ni and Fe required higher pH values and was less efficient than Cu and Zn recovery. In addition, bulk precipitation of metals was also tested by feeding the leach liquor directly to another sulfate-reducing FBR. In order to reduce its toxicity and maintain stable sulfate reduction performance in the FBR, the leach liquor had to be diluted ten-fold and the pH adjusted from 0.6 to approximately 4. Crown
Copper ammonia leaching from smelter slag
International Journal of Biology and Chemistry
Copper smelter slag can be considered as an important source for using in the copper hydrometallurgy. Ammonia leaching seems to be attractive for processing copper slag. Under the influence of ammonia, copper, which is part of the minerals of copper, forms soluble ammonia complexes, while iron precipitates as insoluble compounds. In the present work, the possibility of leaching the copper smelter slag (1.26 wt.% Cu) of the Balkhash smelter using NH 4 OH solutions was considered. The effect of experimental factors (leaching duration, reagent concentration, temperature, stirring rate, as well as a solid-to-liquid ratio) on the extraction of copper into solution was studied. It was found that the extraction of copper into solution increases with increasing temperature (in the studied range 298-333 K), pulp density (up to 10 pct) and stirring rate (up to 800 rpm). The concentration of NH 4 OH almost does not affect on the level of copper extraction in the range of 1-4 M. The following experimental conditions provide the recovery of 65% of Cu into ammonia solution: 1M NH 4 OH, T = 333 K, particle size 90% < 200 mesh, solid-to-liquid ratio 10 pct, stirring rate 800 rpm, and leaching duration 180 min, 65% of copper is extracted into the solution. Shrinking core model with mixture kinetics was used to describe the process of ammonia leaching of copper from smelter slag. The activation energy and pre-exponential factor for the reactions of copper dissolution were calculated to be 16.2 ± 0.7 kJ/mol and 0.138 ± 0.001 min-1 , respectively. The relatively low value of the activation energy indicates that the rate of the overall leaching process is controlled mainly by the processes of mass transfer rather than by the rate of chemical reactions of copper dissolution.
Leaching of lead metallurgical slags and pollutant mobility far from equilibrium conditions
Applied Geochemistry, 2008
Editorial handling by R.B. Wanty a b s t r a c t Lead metallurgical slags are partially vitrified materials containing residual amounts of Zn, Pb, Cr, Cd and As. These hazardous materials are generally buried on heaps exposed to weathering. In this study, leaching behavior of lead blast furnace slags has been tested using pure water and open flow experiments. It appears that in such far from equilibrium and slightly acidic conditions, the main phase to be altered is the vitreous phase. As for lunar, basaltic and nuclear glasses, alkalis/proton exchanges prevail and lead to the formation of a non-protective altered layer enriched in Si, Fe and Al. The composition of the altered layer is quite constant except for Si whose concentration decreases towards the leachate interface. Owing to their sizes, micrometric Pb droplets are not always totally dissolved at the slag surface. Nevertheless, nanometric Pb droplets are instantaneously dissolved while a surrounding altered layer is formed. This leads to high Pb releases in open flow systems. Leachate chemistry and dissolution rates of the vitreous phase are closely comparable to previous leaching tests with basaltic and nuclear glasses in conditions far from equilibrium. Moreover, this study confirms that Fe is a stable element in such conditions.
Remarks on the short-term chemical stability of primary lead smelting slag
Environmental Earth Sciences, 2017
The short-term leaching behavior of a landfilled primary Pb smelter slag from the Santo Amaro (Brazil) smelter was investigated using about 1-day contact time with acid and alkaline solutions. Strong alteration of this slag was observed only below pH 3. In this extreme environment, in addition to the previously discussed behavior of Ca, Si, Fe, Pb and Zn, the As, Cd and Cu were solubilized; however, due to the small content of these elements in the slag, the solution has low content of them. The hierarchical cluster analysis of the results of several leaching tests shows that Pb, As and Cd are part of a group related to the metallic lead phase trapped in the matrix. There is a second group related to some components of the slag matrix (Zn, Ca and Fe) likely oxides; and Si alone is part of a third group related to the slag matrix. The sequential leaching experiments indicate that the main lead solubilization is related to the oxidant environment which confirms the predominance of lead as metallic particles inside the large particles of the slag matrix. These results indicate that, despite the fact that the landfilled slag removal is needful, it is a secondary task to reduce the contamination risk of the region of the former smelter.