Standard Leaching Test Research Articles

Gaps in predicting water quality impacts of unbound air-cooled blast furnace slag utilized for roadway construction

Air-cooled blast furnace slag (ACBFS) is often used as road construction aggregate. Several incidences of adverse environmental effects have been reported in Indiana where unbound slag has been used. The aggregates that caused issues in the field had been previously approved for use by passing State of Indiana standard slag leaching procedures. The study goal was to test several hypotheses posed to the Indiana Department of Transportation and authors by the industry about slag leaching, and to better understand water quality impacts. Ten slags from two suppliers underwent leaching procedures adopted by two U.S. states, but additional test procedures and material and leachate chemical characterization were also conducted to better interpret results. Aggregates varied in size and age (24 h to 2 years old). Like prior literature reports, the chemical composition among the slag samples was similar. However, water quality impacts observed at the bench-scale in this study differed substantially across the slags. Results were consistent with those previously reported at Indiana field sites, but not with literature reported results from standardized leaching tests (i.e., TCLP, percolation, etc.). In the present study, no relationship was found between slag age and leachate composition. Leachate pH, conductivity, and color levels exceeded thresholds of regulatory and aquatic toxicity significance. For one slag, leachate pH reached 12.9, but the effluent was colorless. During both stagnation and rinsing tests, aqueous chloride, sulfate, and zinc concentrations sometimes exceeded regulatory water quality and aquatic toxicity levels. Repeated rinsing of the slag resulted in water conductivity and sulfate concentration differences. To better understand and predict the impacts of unbound ACBFS, additional fundamental studies and field investigations are recommended. Unbound ACBFS is not recommended for use near environmentally sensitive areas, drinking water sources, habituated areas, and where it may have water contact (i.e., waterways, wetlands, reservoirs, and groundwater).

Leaching characteristics of metals from recycled concrete aggregates (RCA) and reclaimed asphalt pavements (RAP)

Recycled concrete aggregates (RCA) and reclaimed asphalt pavements (RAP) are two construction waste products that are commonly used in the road construction industry. Besides many advantages, pollutants leaching from RCA and RAP are highlighted as the most concerning environmental issue. This study investigated metals leaching characteristics from RCA and RAP due to the variations in key influential factors of pH, dissolved organic carbon (DOC), compaction and liquid to solid ratio (L/S). The leaching tests for RCA and RAP were carried out separately and additionally, the standard leaching test was conducted as the benchmark for leaching investigations. Study outcomes revealed that the combined influences of factors are variable for RCA and RAP, while influences are also variable for individual metals. L/S ratios considerably affect the release of metals from RCA under saturated conditions, facilitating high metal concentrations in the leachate. On the other hand, acidic solutions are more favourable for leaching of metals from RAP. The influence of DOC in solution was minimal on the metal leachability. Interestingly, the increased degree of compaction with a higher density of materials presented the highest negative influence on metal leachability, suggesting that the metal leachability can significantly reduce, in particular when the RCA and RAP are used for the sub-base layers of road structure with a higher degree of compaction. However, the use of these recycled materials under field conditions should be further studied as there is an increasing concern of metal leaching from RCA and RAP with respect to recreational and drinking water thresholds.

Towards circular and sustainable restoration of a deeply polluted river basin: The Odiel River catchment (SW Spain)

The Ría de Huelva estuary located in SW Spain is heavily polluted by acid mine drainage leachates and phosphate fertilizer industry effluents. This study assesses the effectiveness of a solid waste rich in calcite originated during the remediation of industrial effluents using the passive dispersed alkaline substrate (DAS) technology, for the treatment of highly acid and polluted mine drainages. The research consists of flowing the mine leachates through a column loaded with a combination of an alkaline reagent (i.e., calcite-rich waste resulting from the treatment of industrial leachates) scattered in a non-reactive matrix (i.e., wood chips) to increase the pH of acidic water while decreasing the solubility of dissolved pollutants. The alkaline treatment achieved average removal percentages of 100 % for Al and Fe, and close to 90 % for Cu. However, the treatment was not effective for other metals present in mine drainages such as Co and Ni. These results are comparable to those achieved in the DAS treatment with commercial limestone. The precipitation of oxyhydroxysulfates (i.e., schwertmannite and basaluminite) and carbonates (i.e., malachite and hydrozincite) minerals could be controlling the solubility of pollutants during the treatment. The solid wastes from the DAS treatment were subjected to two standardized leaching tests (EN 12457-2 from the European Union and toxicity characteristic leaching procedure (TCLP) from the United States) in order to ensure suitable management and avoid potential environmental impacts. According to European Union legislation, the high mobility of Cu, Zn and SO4 confers some solid wastes from the DAS treatment the hazardous waste classification. However, according to United States regulation, these same solids are considered non-hazardous wastes. This research could help to improve the environmental sustainability of acid mine drainage treatment with DAS technology by replacing marketable limestone with a low-cost alkaline waste.

Physicochemical Properties and Leaching Toxicity Assessment of Jarosite Residue

The safe disposal of hazardous waste from zinc hydrometallurgy, such as jarosite residue, is crucial for the sustainable development of the industry. The chemical, structural and morphological properties of jarosite residue from zinc smelting were studied by a combination of various characterizations, and environmental stability was evaluated using the toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT) and long-term leaching experiments (LTLE). Phase composition analysis revealed that zinc ferrite and sodium jarosite were the main phases present in the jarosite residue. TCLP and CSLT analyses indicated that the Zn and Pb contents exceeded their respective toxicity identification standards by more than 30 times and 8 times, respectively, exceeding the threshold values of the standard. The LTLE results demonstrated that Pb concentrations continued to exceed the standard limits, even after long contact times. This study has paramount significance in the prediction of jarosite residue stability and the evaluation of its potential for secondary environmental pollution.

Case Study on Secondary Building Materials for a Greener Economy

Half of global material consumption involves mineral material. The circularity is still low so that the enhanced use of secondary building material is required to close loops. Three different secondary building materials are discussed based on exemplary research results: construction and demolition waste (C&D waste), soil-like material, and incineration bottom ash (IBA). Focus was placed on the environmental compatibility of the materials examined mainly by standardized leaching tests. C&D waste was investigated after a wet treatment using a jigging machine, and soil-like material and IBA were characterized with respect to their material composition. Their environmental compatibilities in particular were studied using standard leaching tests (batch tests and column tests). It was concluded that soil-like material can mostly be utilized even when the precautionary limit values set are exceeded by a factor of less than two. For C&D waste, the fine fraction below 2 mm and the content of brick material is problematic. IBA fulfills quality level “HMVA-2” following German regulations. Improved levels of utilization might be achievable with better treatment technologies.

The Synthesis of Lead-Bearing Jarosite and Its Occurrence Characteristic and Leaching Toxicity Evaluation

Lead is the main toxic factor in jarosite residue. It is important to study the release behavior of lead from simulated lead-bearing jarosite (SLBJ) for predicting the stability of jarosite residue and its secondary pollution to the environment. To identify the technical issues and limitations associated with its safe disposal, a comprehensive analysis of the chemical, structural, and morphological characteristics of SLBJ was conducted using various detection techniques including XRF, XRD, SEM-EDS, FTIR, XPS, etc. The environmental stability of SLBJ was assessed through the toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT), and a long-term leaching experiment (LTLE). Phase composition analysis revealed that the primary components of SLBJ are sodium jarosite and lead sulfate. TCLP and CSLT results indicated that lead content surpassed the toxicity identification standard limit by more than 47 times. Furthermore, LTLE indicated that the lead concentration surpassed the standard limit about 15 times after prolonged contact time. This study is of great significance for predicting the stability of jarosite residue and its secondary pollution to the environment.

Investigating the ecotoxicity of construction product eluates as multicomponent mixtures

BackgroundThe release of hazardous compounds from construction products can harm human health and the environment. To improve the sustainability of construction materials, the leaching of substances from construction products and their potential environmental impact should be assessed. Twenty-seven construction products from different product groups were examined with a combination of standardized leaching tests (dynamic surface leaching test and percolation test) and biotests (algae, daphnia, fish egg, luminescent bacteria, umu and Ames fluctuation tests). To identify the released substances, extensive qualitative and quantitative chemical analyses were performed, including gas chromatographic and liquid chromatographic screening techniques.ResultsMany of the tested eluates caused significant ecotoxic effects. Particularly high ecotoxicities were observed for grouts (lowest ineffective dilution (LID) up to 16384) and cork granules (LID up to 24578). The results of ecotoxicity tests allow the prioritization of the eluates that should be subjected to detailed chemical analyses. Organic screening by different methods and ranking the identified substances based on recorded hazard classification is a suitable approach to identify the relevant toxic substances.ConclusionsDetermining the ecotoxicity of eluates from construction products records the summary effect of all leachable substances. This instrument is especially useful for construction products of complex and largely unknown composition. The ecotoxicological and the chemical–analytical approach complement each other in an ideal way to characterize the potential hazard of eluates from construction products and to identify the environmentally hazardous components in these eluates. Our results confirm that the proposed harmonized methods for testing eluate toxicity are an adequate and applicable procedure to move toward a more sustainable way of building and to reduce toxic effects of construction products in their use phase in the environment..

Mechanical performance and microstructural properties of cement mortars containing MSWI BA as a minor additional constituent

Along with an increase in the amount of municipal waste being incinerated, the amount of Municipal Solid Waste Incineration Bottom Ash (MSWI BA) is growing every year. Combined with limited landfill sites in the Netherlands, this necessitates new applications for the MSWI BA disposal. The larger MSWI BA fractions (> 3 cm) can be successfully used as a natural aggregate substitute in concrete. At the same time, the fine MSWI BA fraction (< 3 cm) has several drawbacks (high porosity, high contaminant content, metallic aluminum, etc.), which make it difficult to use this way. However, if this fine MSWI BA fraction is subjected to treatment that eliminates these shortcomings, it can become a product suitable as a Minor Additional Constituent (MAC) for cement (< 5 % w/w). The addition of MAC allows to use less cement without having a negative influence on its properties, therefore reducing the carbon footprint, and utilizing suitable waste materials (instead of landfilling them). In this paper, mortars and pastes containing the decontaminated (by sieving out the most contaminated fraction < 125 µm) and mechanically treated MSWI BA < 3 mm was used as a cement replacement in the range of 0–20 %. Three types of milled fines were studies, two of them had a particle-size distribution close to CEMI 42.5 and 52.5 to determine the optimum percentage of cement replacement, while the third was not optimized. Effects of MSWI BA fine replacements were studied in terms of mechanical properties, hydration (isothermal calorimetry), microstructure (optical microscopy), and the environmental impact (the standard leaching test by ICP–AES and ion chromatography). The results showed that the mildly milled fines, with a cement replacement of 1 %, are most suitable as a MAC as they have the lowest environmental impact, and no negative effects on the mechanical properties (compressive strength).

Valorization Potential of Polish Laterite Leaching Residues through Alkali Activation

In this study, the valorization potential of Polish laterite leaching residues through alkali activation with the use of NaOH and Na2SiO3 solutions as activators was investigated. The effect of the main factors, namely the H2O/Na2O molar ratio in the activating solution, the curing temperature, and the ageing period on the main properties of the produced alkali activated materials (AAMs) was assessed. The experimental results showed that AAMs with sufficient compressive strength were only produced when the laterite leaching residues were mixed with significant quantities of metakaolin; thus, when the mass ratio of laterite leaching residues and metakaolin was 0.50, after curing at 40 °C for 24 h and ageing for 7 days, the produced AAMs acquired compressive strength that slightly exceeded 25 MPa. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy (SEM–EDS) analysis were used for the characterization of the raw materials and selected AAMs. Furthermore, the structural integrity of the specimens was investigated after immersion in distilled water and acidic solution (1 mol L−1 HCl), or after firing at higher temperatures. Finally, the toxicity of the produced AAMs was assessed with the use of standard leaching tests.

Chemical Stabilization Used to Reduce Geogenic Selenium, Molybdenum, Sulfates and Fluorides Mobility in Rocks and Soils from the Parisian Basin

Rocks and soils excavated from civil works frequently present high concentrations of naturally occurring leachable (oxy-)anions. This situation raises concerns regarding the potential transfer of contaminants to groundwater in a storage scenario. This study was carried out to give practical insights on the ability of various stabilizing agents to reduce molybdenum (Mo), selenium (Se), fluorides and sulfates mobility in four types of naturally contaminated excavated materials. Based on standardized leaching tests results, Mo and Se were effectively immobilized after zero valent iron or iron salts additions. Although alkaline materials were found to effectively reduce fluorides and sulfates mobility, their addition occasionally caused a subsequent increase in Mo and Se leaching due to pH increase. None of the reagents tested allowed a simultaneous immobilization of all (oxy-)anions sufficient to reach regulatory threshold values. The remaining difficulties were related to: (i) sulfates leaching from gypsum-rich samples, (ii) fluorides leaching from clayey samples and (iii) Mo and sulfates mobility from tunnel muck. Altogether, the study revealed that the choice of stabilizing agents should be made depending on the speciation of the contaminant or else an opposite impact (i.e., increase in contaminant mobility) might be triggered.

Physicochemical and environmental characteristics of alkali leaching residue of wolframite and process for valuable metals recovery

Physicochemical and mineralogical characteristics of an alkali leaching residue of wolframite were studied by XRD, SEM−EDS, chemical phase analysis, mineral liberation analyzer (MLA), and TG−DSC methods. Batch leaching tests, toxicity characteristic leaching procedure (TCLP) tests and Chinese standard leaching tests (CSLT) were conducted to determine the environmental mobility of toxic elements. The results show that, due to the high contents of W, Fe, Mn, Sn, and Nb, the residue is with high resource value, but the content of a toxic element, As, is also high. The existing minerals of the investigated elements mainly occur as monomer particles, but it is difficult to extract these valuable metals by conventional acid leaching due to their mineral properties. The release of As increases over time in acidic environment. The leaching concentration of all investigated harmful elements through TCLP is within the limiting value, while the leaching concentration of As through CSLT exceeds the limiting value by more than 4 times, so the residue is classified as hazardous solid waste based on the Chinese standard. A process for valuable metals recovery from this residue was proposed. Preliminary experimental results indicated that the main valuable metals could be extracted effectively.

Tree species-based differences vs. decay performance and mechanical properties following chemical and thermal treatments

Many thermal and chemical treatments are known to inhibit wood decay despite the wood grade processed, but their impact, e.g., chemicals’ leaching and decay resistance, may not be similar. The aim of this study was to test whether some model treatments retain their performance in different wood species. Additionally, the effects of thermal modification and linseed oil-based varnish treatments as means to mitigate water-soluble chemicals leaching were assessed. The mass loss caused by Trametes versicolor was measured after a 12-week exposure to analyze whether the different treatment approaches prevented the fungal decay after a standard leaching test. The mechanical properties before and after exposure were tested independently to determine whether the mechanical properties of different wood species were affected by the tested treatments and wood decay. The responses of the tested wood species were found to vary by treatments, but thermal and chemical fixation methods for water-soluble tannins were beneficial in all cases considering the mass loss and the degradation of modulus of rupture and modulus of elasticity of treated wood. Varnish was overall the most effective treatment against decay, but the results emphasize the need for testing potential preservation methods and chemicals on several species.

Tailored Leaching Tests as a Tool for Environmental Management of Mine Tailings Disposal at Sea

The expanding human activities in coastal areas increase the need for developing solutions to limit impacts on the marine environment. Sea disposal affects the marine environment, but despite the growing knowledge of potential impacts, there are still no standardized leaching tests for sea disposal. The aim of this study was to contribute to the development of leaching tests, exemplified using mine tailings, planned for submarine disposal in the Repparfjord, Norway. The mine tailings had elevated concentrations of Ba, Cr, Cu, Mn and Ni compared to background concentrations in the Repparfjord. Variables known to affect metal leaching in marine environments (DOC, pH, salinity, temperature, aerated/anoxic) were studied, as was the effect of flocculant (Magnafloc10), planned to be added prior to discharge. Stirred/non-stirred setups simulated the resuspension and disposal phases. Leaching of metals was below 2% in all experiments, with the highest rate observed for Cu and Mn. Multivariate analysis revealed a different variable importance for metals depending on their association with minerals. Higher leaching during resuspension than disposal, and lower leaching with the addition of Magnafloc10, especially for Cu and Mn, was observed. The leaching tests performed in this study are transferable to other materials for sea disposal.

Environmental management and potential valorization of wastes generated in passive treatments of fertilizer industry effluents

A phosphogypsum stack located in SW Spain releases highly acidic and contaminated leachates to the surrounding estuarine environment. Column experiments, based on a mixture of an alkaline reagent (i.e., MgO or Ca(OH)2) dispersed in an inert matrix (dispersed alkaline substrate (DAS) technology), have shown high effectiveness for the treatment of phosphogypsum leachates. MgO-DAS and Ca(OH)2-DAS treatment systems achieved near total removal of PO4, F, Fe, Zn, Al, Cr, Cd, U, and As, with initial reactive mass:volume of leachate treated ratios of 3.98 g/L and 6.35 g/L, respectively. The precipitation of phosphate (i.e., brushite, cattiite, fluorapatite, struvite and Mn3Zn(PO4)2·2H2O) and sulfate (i.e., despujolsite and gypsum) minerals could control the solubility of contaminants during the treatments. Therefore, the hazardousness of these wastes must be accurately assessed in order to be properly managed, avoiding potential environmental impacts. For this purpose, two standardized leaching tests (EN-12457-2 from the European Union and TCLP from the United States) were performed. According to European Union (EN-12457-2) regulation, some wastes recovered from DAS treatments should be classified as hazardous wastes because of the high concentrations of SO4 or Sb that are leached. However, according to United States (US EPA-TCLP) legislation, all DAS wastes are designated as non-hazardous wastes. Moreover, the solids generated in the DAS systems could constitute a promising secondary source of calcite and/or P. This research could contribute to worldwide suitable waste management for the fertilizer industry.

Environmental Impact of Construction Products on Aquatic Systems—Principles of an Integrated Source–Path–Target Concept

Buildings exposed to water can release undesirable substances which, once transported to environmental compartments, may cause unwanted effects. These exposure pathways need to be investigated and included in risk assessments to safeguard water quality and promote the sustainability of construction materials. The applied materials, exposure conditions, distribution routes and resilience of receiving compartments vary considerably. This demonstrates the need for a consistent concept that integrates knowledge of emission sources, leaching processes, transport pathways, and effects on targets. Such a consistent concept can serve as the basis for environmental risk assessment for several scenarios using experimentally determined emissions. Typically, a source–path–target concept integrates data from standardized leaching tests and models to describe leaching processes, the distribution of substances in the environment and the occurrence of substances at different points of compliance. This article presents an integrated concept for assessing the environmental impact of construction products on aquatic systems and unravels currently existing gaps and necessary actions. This manuscript outlines a source–path–target concept applicable to a large variety of construction products. It is intended to highlight key elements of a holistic evaluation concept that could assist authorities in developing procedures for environmental risk assessments and mitigation measures and identifying knowledge gaps.

Surface Tuning of Wood via Covalent Modification of Its Lignocellulosic Biopolymers with Substituted Benzoates-A Study on Reactivity, Efficiency, and Durability.

Chemical modification of wood applying benzotriazolyl-activated carboxylic acids has proven to be a versatile method for the durable functionalization of its lignocellulosic biopolymers. Through this process, the material properties of wood can be influenced and specifically optimized. To check the scope and limitations of this modification method, various benzamide derivatives with electron-withdrawing (EWG) or electron-donating (EDG) functional groups in different positions of the aromatic ring were synthesized and applied for covalent modification of Scots pine (Pinus sylvestris L.) sapwood in this study. The bonded amounts of substances (up to 2.20 mmol) were compared with the reactivity constants of the Hammett equation, revealing a significant correlation between the modification efficiency and the theoretical reactivity constants of the corresponding aromatic substitution pattern. The successful covalent attachment of the respective substituted benzamides was proven by attenuated total reflection infrared (ATR-IR) spectroscopy, while the stability of the newly formed ester bond was proven in a standardized leaching test.

Long-term stability of arsenic calcium residue (ACR) treated with FeSO4 and H2SO4: Function of H+ and Fe(Ⅱ)

Arsenic calcium residue (ACR) generated from the As-bearing wastewater treatment is highly hazardous due to high content of available As, which was seeking a suitable method for safe disposal such as stabilization treatment. In this study, the stabilization of available As in ACR was performed by combined treatment with FeSO4 and H2SO4. After stabilization treatment, the As leaching concentrations extracted by China Standard Leaching Test (CSLT, HJ/T299-2007) decreased significantly from 162 mg/L to less than the Chinese regulation limit of 1.2 mg/L. And FeSO4-H2SO4 treated ACR could maintain good long-term stability even after cured for 365 days. The stabilization mechanism for available As in ACR using leaching tests, sequential extraction analysis, XPS, XRD, and SEM-EDS was investigated. H+ from H2SO4 and Fe(Ⅱ) hydrolysis was committed to the full release of available As. Reactive oxygen species (ROSs) produced from Fe(Ⅱ) oxygenation drove the oxidation of As(Ⅲ) to As(Ⅴ). The release As was stabilized by forming stable Fe-O-As complexes (FeAsO4·xFe(OH)3). Moreover, this study also presented an effective and feasible method for ACR disposal.

Roof runoff contamination: Establishing material-pollutant relationships and material benchmarking based on laboratory leaching tests

Because roofs represent a major part of the urban impervious surface, it is hypothesized that roof runoff is an important source of urban stormwater contamination. However, the contribution of different roofing materials to this contamination has only been examined to a limited extent. In this study, a resource and time efficient methodology, which uses some of the principles of a standardized leaching test (CEN/TS16637-2), was developed to identify material-pollutant relationships for sixteen commonly used roofing materials (EPDM, PVC, TPO, EVA, PU and bitumen membranes). Metals were detected in concentrations ranging from several μg/L in the leachate of synthetic materials up to 2.5 mg/L for Zn in the leachate of EPDM materials. Cd and Cr were not detected in any of the leachates. Furthermore, polycyclic aromatic hydrocarbons were detected in most leachates, with phenanthrene and naphthalene being most frequently detected in concentrations up to 4.5 μg/L for naphthalene. Further insights on organic pollutants’ leaching from the tested materials were obtained by a non-target GC-MS screening of the leachates. Several commonly used additives such as flame retardants and light stabilizers were detected. Although no information on long-term leaching and material behavior under outdoor conditions could be obtained by the developed methodology, the laboratory test results could be used to benchmark the materials for their potential impact on roof runoff quality by the calculation of material indexes (which summarize the material-pollutant relationships). EPDM and PU roofing materials were identified as the materials having the highest potential to affect roof runoff quality.

Thermal evolution effects on the properties of converting Cs-polluted soil into pollucite-base glass-ceramics for radioactive cesium immobilization

The Fukushima nuclear accident in Japan on March 11, 2011, produced large amounts of Cs-polluted soil which must be controlled to prevent the spread of hazardous Cs into the environment. In this paper, the effects of heat treatment on the structure and properties of Cs-containing glass-ceramics, as a simulated nuclear waste form, were systematically investigated. Cesium atoms are chemically bonded in the pollucite structure, and the amorphous phase further encapsulates the pollucite crystals in the glass-ceramics, thus providing an extra protective layer for the immobilized Cs. XRD analysis, Raman and FT-IR studies on the glass-ceramics synergistically indicated that the optimum crystallization temperature for pollucite is around 1000 °C. The pollucite is predominantly the main crystalline phase with a narrow crystal size distribution between 0.5 and 2 μm. Standard leaching test results show that the leaching rate of Cs was very low (3.0 × 10−3 g/(m2·d)). The study offers a practical method for immobilizing Cs in pollucite-base glass-ceramics. Moreover, the experimentally obtained data may provide some important references for converting Cs-polluted soil into pollucite-base glass-ceramics waste form.

The application of citric acid solutions for selective removal of zinc from steelmaking dust

Steelmaking dust is one of the wastes which are produced by ironworks. This kind of waste is a byproduct produced mainly in electric arc furnace. Zinc content in dust is different and depends on the charge processed in the furnace. The basic technology used for recycling steelmaking dust is Waelz process, however, it requires a large amount of reducer and generates a lot of waste which needs to be stored. First stage in this study was to analyze if steelmaking dust was safe to be exposed to atmospheric conditions. To verify this, the dust was subjected to two kinds of standard leaching tests, TCLP and EN-12457-2. The amount of extracted elements was considerable and that was why steelmaking dust should be treated as dangerous waste. Leaching in citric acid solutions was divided in four series. The first one was set to determine the time and temperature for most selective zinc leaching. Next series optimized three leaching parameters which were: citric acid concentration, liquid to solid phase ratio (l/s), and the stirring speed. Performed experiments showed the optimal conditions for selective leaching: temperature of 50?C, leaching time of 60 minutes, citric acid concentration of 0.5 mol/dm3, l/s ratio of 10, and stirring speed of 250 rpm.