Leaching Medium Research Articles

A comparative study of the kinetics of the oxidation of iron(II) by oxygen in acidic media - mechanistic and practical implications

Abstract The results of this comparative study have shown that in 1 M acid solutions, the differences in reactivity of iron(II) for reduction of oxygen are within about an order of magnitude of each other for the systems studied at 40 °C. This applies to both the uncatalysed and copper(II) catalysed systems. The exception is the chloride system in which the rate can be significantly increased by increasing the chloride concentration. The other main conclusion is that although catalysis by copper(II) ions can be significant there exist conditions (iron(II) and (III) concentrations) for which the effect is not that important. Rate equations for both the uncatalysed and catalysed reactions have been derived that apply equally to all the systems studied. Values for the various rate constants have been obtained by analysis of extensive kinetic data in 1 M acid solutions at 40 °C. A limited electrochemical study has been used to derive values for the equilibrium constant for the reaction involving the iron(III)/iron(II) and copper(II)/copper(I) couples. An attempt has been made to compare relevant constants with previously published data and to derive a mechanism that is consistent with the kinetic results. This study has shown that the use of methanesulfonic acid as an oxidative leaching medium does not offer any advantages and is the least reactive of the systems studied.

Development of complementary CE-MS methods for speciation analysis of pyrithione-based antifouling agents.

In the recent decade, metal pyrithione complexes have become important biocides for antifouling purposes in shipping. The analysis of metal pyrithione complexes and their degradation products/species in environmental samples is challenging because they exhibit fast UV degradation, transmetalation, and ligand substitution and are known to be prone to spontaneous species transformation within a chromatographic system. The environmental properties of the pyrithione species, e.g., toxicity to target and non-target organisms, are differing strongly, and it is therefore inevitable to identify as well as quantify all species separately. To cope with the separation of metal pyrithione species with minimum species transformation during analysis, a capillary electrophoresis (CE)-based method was developed. The hyphenation of CE with selective electrospray ionization- and inductively coupled plasma-mass spectrometry (ESI-, ICP-MS) provided complementary molecular and elemental information for the identification and quantification of pyrithione species. To study speciation of pyrithiones, a leaching experiment of several commercial antifouling paints containing zinc pyrithione in ultrapure and river water was conducted. Only the two species pyrithione (HPT) and dipyrithione ((PT)2) were found in the leaching media, in concentrations between 0.086 and 2.4μM (HPT) and between 0.062 and 0.59μM ((PT)2), depending on the paint and leaching medium. The limits of detection were 20nM (HPT) and 10nM ((PT)2). The results show that complementary CE-MS is a suitable tool for mechanistical studies concerning species transformation (e.g., degradation) and the identification of target species of metal pyrithione complexes in real surface water matrices, laying the ground for future environmental studies. Graphical abstract Hyphenation of CE with ESI- and ICP-MS provided complementary molecular and elemental information. Metal pyrithione species released from commercial antifouling paints could be identified and quantified in ultrapure and river water matrices.

Selective Leaching of Rare Earth Elements (REEs) from Eudialyte Concentrate after Sulfation and Thermal Decomposition of Non-REE Sulfates

Eudialyte, a sodium rich zirconosilicate, is one of the promising sources for REEs (rare earth elements), particularly for HREEs + Y (heavy rare earth elements and yttrium). The key challenge in hydrometallurgical processing is the prevention of silica gel formation and REE separation from resulting multi-element leach solutions. This study deals with the selective extraction of REE from eudialyte concentrate by selective roasting. In this method, metal ions are converted into sulfates, followed by the decomposition of non-REE sulfates in a roasting step and the water leaching of the calcine. The effect of acid addition, roasting temperature, roasting time, pulp density and leaching time is studied. For sufficient conversion of REEs into sulfates, sulfuric acid is added in excess. At a roasting temperature of ≥750 °C sulfates of zirconium, hafnium, niobium, aluminum and iron decompose into sparingly soluble compounds, while REE and manganese sulfates remain stable up to a roasting time of 120 min. The silica present in the calcine is found to be metastable even after roasting. The amount of leached Si4+ is dependent predominantly on the pH value of the leaching medium. Applying the method, REEs can be efficiently separated from zirconium, hafnium, niobium, aluminum and iron. However, only diluted solutions can be produced. Water leaching of calcine at high solid/liquid ratios causes REE losses resulting from formation of double sulfates and gypsum. The acid excess removed from the reaction mixture in the roasting stage can be simply recovered by treatment of the gas phase.

A comparative study of the extraction of metals from the spent fluid catalytic cracking catalyst using chemical leaching and bioleaching by Aspergillus niger

Abstract The present study evaluates biopotential of Aspergillus niger and chemical potency of strong organic and inorganic acids to leach out Al, Fe, Ti, Ni, V from spent fluid catalytic cracking catalyst (SFCCC). One-step bioleaching (OSBp) and spent medium bioleaching (SMB) of metals at 1%, 3% and 5% pulp densities by Aspergillus niger was investigated. Leaching efficiency was found to be maximum at 1% pulp density and decreased as the pulp density increased to 5%, this is perhaps due to the inhibitory effect of some metals existing in SFCCC. The maximum amount of Al, Fe, Ti, Ni, and V leached from SFCCC are 1388 mg/L, 28 mg/L, 6 mg/L, 2 mg/L and 8 mg/L of leaching medium respectively. Biologically produced leaching agents other than citric, gluconic and oxalic acids produced by Aspergillus niger solely contributed to 50%, 32%, and 42% of Al, Ti and V leaching efficiencies respectively. The acidic pH in OSBp suggests acidolysis as the leading leaching mechanism. The citric acid is the chief leaching agent produced by Aspergillus niger in the presence of SFCCC while gluconic acid dominated in SMB (in the absence of SFCCC). OSBp yielded higher leaching efficiencies of all the metals compared to SMB. OSBp dominated Al, Ti, and V leaching compared to all organic and inorganic acid leaching. While OSBp of Fe was comparable to inorganic acid leaching and oxalic acid leaching is suggested for Ni leaching. The competitive Al, Ti, V and Fe leaching and being environmentally friendly, OSBp of metals from SFCCC by Aspergillus niger is recommended.

THE USE OF CHEMICALLY MODIFIED PLANT MATERIALS AS SOIL BUILDERS

The results of studies on the effects of composite polymer preparations obtained by carboxymethylation of various types of plant materials (sawdust common pine (Pinus silvestris) (NaKMD preparation), oat flower films (Avena sativa L.) (NaKMO preparation) and sunflower husk (Helianthus annuus L.) (NaKMP preparation)), on the water resistance of soil aggregates in laboratory and field conditions of the forest-steppe of the Altai Territory are presented. The object of research is ordinary and leached medium loamy black earth. The water resistance index of soil aggregates was determined by the method of P.I. Andrianova. It was found that both in laboratory and in field conditions, soil aggregates with the use of drugs are washed out by water much more slowly than in versions without the use of drugs. The NaCMP preparation, which contains the largest amount of carboxymethylated lignin (17.1%), had the greatest influence on the resistance of soil aggregates to water. In general, the water resistance of the soil when using the studied drugs, depending on the application dose, increased 1.2–3.5 times compared to the control. The positive effect of preparations from carboxymethylated plant materials varies in the following order: NaKMP> NaKMO> NaKMD.

Effect of Surface Modification with Different Acids on the Functional Groups of AF 5 Catalyst and Its Catalytic Effect on the Atmospheric Leaching of Enargite

Carbon-based catalysts can assist the oxidative leaching of sulfide minerals. Recently, we presented that AF 5 Lewatit® is among the catalysts with superior enargite oxidation capacity and capability to collect elemental sulfur on its surface. Herein, the effect of acid pre-treatment of the AF 5 catalyst was studied on the AF 5 surface, to further enhance the catalytic properties of AF 5. The AF 5 catalyst was pretreated by hydrochloric acid, nitric acid and sulfuric acid. The results showed that the acid treatment drastically changes the surface properties of AF 5. For instance, the concentration of quinone-like functional groups, which are ascribed to the catalytic properties of AF 5, is 45.4% in the sulfuric acid pre-treatment AF 5 and only 29.8% in the hydrochloric acid-treated AF 5. Based on the C 1s X-ray photoelectron spectroscopy (XPS) results the oxygenated carbon is 30.6% in the sulfuric acid-treated AF 5, 29.2% in the nitric acid-treated AF 5 and 28.3% in the hydrochloric acid-treated AF 5. The nitric acid pre-treated AF 5 resulted in the highest copper recovery during the oxidative enargite leaching process, recovering 98.8% of the copper. The sulfuric acid-treated AF 5 recovered 97.1% of the enargite copper into the leach solution. Among different leaching media and pre-treatment the lowest copper recovery was achieved with the HCl pre-treated AF 5 which was 88.6%. The pre-treatment of AF 5 with acids also had modified its elemental sulfur adsorption capacity, where the sulfur adsorption on AF 5 was increased from 30.9% for the HCl treated AF 5 to 51.1% for the sulfuric acid-treated AF 5.

Column leaching of low-grade saprolitic laterites and valorization of leaching residues

Socio-economic data on nickel and cobalt show their importance throughout the entire metal value chain, from mining to end use, disposal and recycling. Thus, the extraction of both metals from primary and secondary raw materials as well as from wastes is currently considered strategically important for the industry and the society. In this paper heap leaching of Greek low-grade saprolitic laterites, with Ni content 0.97%, was investigated. The main parameters studied involved the strength of the H2SO4 solution used (49 and 147gL-1) and the effect of adding sodium sulfite (Na2SO3) in the leaching medium. The pregnant leach solution (PLS) was recycled several times during leaching in order to minimize acid consumption. The experimental results showed that within a period of 25days, and under the optimum conditions (147gL-1 H2SO4 and 20gL-1 Na2SO3), i) Ni and Co extractions were 72.5% and 47.4%, respectively and ii) Fe and Al co-extractions were 8.7% and 31.3%, respectively. Furthermore, valorization of the leaching residues through alkali activation using NaOH and Na2SiO3 and the addition of metakaolin (MK) for the production of inorganic polymers (IPs) was explored. X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Differential scanning calorimetry (DSC/TG) and Scanning electron microscopy (SEM-EDS) were used to characterize the ore, its leaching residues and the IPs. The IPs produced demonstrated high compressive strength, almost 40MPa and are suitable for a wide range of applications in the construction sector.

A cleaner and efficient process for extraction of vanadium from high chromium vanadium slag: Leaching in (NH4)2SO4-H2SO4 synergistic system and NH4+ recycle

Abstract A cleaner and novelty leaching medium, (NH4)2SO4-H2SO4 synergistic system was introduced into the leaching process for extracting vanadium efficiently after calcification roasting with high chromium vanadium slag (HCVS), and then V2O5 was prepared after precipitation and roasting. The effects of leaching and precipitation conditions were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). 93.45% vanadium and 0.24% chromium were leached when the calcification roasted sample was leached in the (NH4)2SO4-H2SO4 synergistic system at 20 °C for 60 min with a liquid–solid ratio (L/S) of 10, achieving the efficient separation of vanadium and chromium in HCVS. The optimal (NH4)2SO4-H2SO4 synergistic system was composed with 250 g/L (NH4)2SO4 and 3.75 mol/L H2SO4, the amount of H2SO4 was 1 mL in every 30 mL leaching system. The introduction of (NH4)2SO4 provided much NH4+, which could promote the acid leaching reaction. 99.75% vanadium was precipitated further from vanadium-containing leaching liquid when heating the liquid at 60 °C for 60 min after adjusting the system pH at 8.0, and the deposit was ammonium polyvanadate (NH4)2V6O16. Then, V2O5 with a purity of 95.71% was prepared after roasting, and recovery rate of vanadium from HCVS was higher than 93%. After precipitation, the supernatant containing a large amount of NH4+ could be recycled as the new leaching medium with some (NH4)2SO4 adding according to NH4+ loss after vanadium precipitation. This process achieved the efficient extraction of vanadium from HCVS and provided a new thinking for the leaching process based on the (NH4)2SO4-H2SO4 synergistic system.

A bio-hydrometallurgical approach towards leaching of lanthanum from the spent fluid catalytic cracking catalyst using Aspergillus niger

Abstract Spent fluid catalytic cracking catalysts (SFCCC) are the wastes generated from oil refineries, which accounts for 700,000–900,000 metric ton/year worldwide. Lanthanum, a short-term near critical element is the key component of SFCCC and accounts for 8170 mg/Kg. The current research intends to recover lanthanum from SFCCC by Aspergillus niger and compare the results with strong organic and inorganic acid leaching. Batch studies of one-step bioleaching (OSB) at 1, 3 and 5% pulp densities yielded 63%, 52%, and 33% lanthanum recovery, respectively. The decrease in leaching efficiency with an increase in pulp density may be attributed to the inhibition effect of SFCCC on A. niger. Citric acid was the main lixiviant produced by A. niger, whose production was triggered by SFCCC at ≤1% pulp density. Acidic pH of the leaching medium suggested acidolysis as the key mechanism. Cell-free spent medium bioleaching (cfSMB) resulted in 30.8% leaching recovery, which was significantly less than the OSB. In chemical leaching, sulfuric and nitric acid showed 38% efficiency whereas oxalic acid showed 5% recovery. Hydrochloric, citric and gluconic acids resulted in 68%, 65%, and 64% leaching recoveries, respectively, which is nearly the same as that offered by OSB. OSB being the greener process, suggested for lanthanum leaching from SFCCC over other processes.

Leaching behavior and kinetics of vanadium extraction from vanadium-bearing steel slag

The vanadium-bearing steel slag as solid waste is also one of valuable vanadium-containing resource. Recovering vanadium from the refractory steel slag is a great challenge in the world. A leaching process study using high concentration sodium hydroxide solution was proposed in this laboratory work. The effects of sodium hydroxide concentration, particle size, leaching temperature and the ratio of alkali to slag on the rate of vanadium leaching were determined and the leaching kinetics was presented. It indicates that the leaching rate is highly sensitive to the sodium hydroxide concentration and leaching temperature and increases with increasing temperature and sodium hydroxide concentration. By studying the reaction mechanisms, it was found that the dicalcium silicate, tricalcium silicate and calcium ferrited which co-exist with calcium vanadate in the vanadium-bearing steel slag were gradually exposed and reacted with NaOH media to form Na3VO4. The leaching kinetics was analyzed which indicated that the leaching rate is controlled by the chemical reaction with the apparent activation energy of 51.34 kJ/mol. On the basis of this process, the vanadium can be effectively extracted with a leaching rate of more than 80%. The leaching medium can be recycled. It is an effective and cleaner process for leaching vanadium.

Efficient extraction and separation of vanadium and chromium in high chromium vanadium slag by sodium salt roasting-(NH4)2SO4 leaching

Abstract A novelty process based on sodium salt roasting-(NH4)2SO4 leaching was proposed to extract vanadium and chromium in high chromium vanadium slag (HCVS). V2O5 and Cr2O3 was then prepared. The effects of roasting and leaching conditions on vanadium and chromium extraction behavior were studied systematically and completely. Vanadium precipitation conditions and chromium reduction conditions were optimized further. 94.6% vanadium and 96.5% chromium were extracted when HCVS and Na2CO3 were mixed in the molar ratio of n(Na2CO3)/n(V2O3 + Cr2O3) of 2.5, then leached in 30 g/L (NH4)2SO4 solution. 94.8% vanadium was precipitated as ammonium polyvanadate (APV) just by adjusting the leaching liquid pH at 4.5, almost all chromium was remained in liquid, achieving the efficient separation of vanadium and chromium. Chromium was then recovered by reduction and precipitation. More than 99% chromium was reduced when Na2S2O5 was added in m(Na2S2O5)/m[Cr(VI)] above 3. By roasting the deposits of vanadium and chromium respectively, 91.49% V2O5 and 89.89% Cr2O3 were obtained. The supernatant after vanadium and chromium extraction containing NH4+ could be recycled as the new leaching medium with some new (NH4)2SO4 added, which greatly reduced the discharge of ammonia-nitrogen wastewater and made the whole process more environmentally friendly.

Sodium fluoride assisted acid leaching of coal fly ash for the extraction of alumina

Abstract Coal fly ash, generated in thermal power plants was processed through sulphuric acid leaching for the extraction of alumina. Both fly ash and alkali treated fly ash residue, obtained after partial removal of silica, were leached in sulphuric acid medium. Solubilisation of alumina in the acidic medium was found to be more efficient while processing the alkali treated fly ash residue as compared to the fly ash. The effect of addition of sodium fluoride (NaF) on leaching of alumina was examined at varied acid concentrations, temperatures, and time of leaching. A marked improvement in leaching recovery for alumina was observed due to the addition of NaF in the acidic leaching medium. XRD pattern of the leach residue confirmed that the alumina bearing phase i.e. mullite got dissociated in the presence of fluoride ions releasing alumina to the leaching medium for which a significant improvement in leaching efficiency was observed. A process flowsheet has been developed for the extraction of alumina from fly ash and production of a by-product, calcium silicate, for the regeneration of NaOH to make the process industrially viable.

Comparison of Ultrasound-Assisted and Regular Leaching of Vanadium and Chromium from Roasted High Chromium Vanadium Slag

Ultrasound-assisted leaching (UAL) was used for vanadium and chromium leaching from roasted material obtained by the calcification roasting of high-chromium–vanadium slag. UAL was compared with regular leaching. The effect of the leaching time and temperature, acid concentration, and liquid–solid ratio on the vanadium and chromium leaching behaviors was investigated. The UAL mechanism was determined from particle-size-distribution and microstructure analyses. UAL decreased the reaction time and leaching temperature significantly. Furthermore, 96.67% vanadium and less than 1% chromium were leached at 60°C for 60 min with 20% H2SO4 at a liquid–solid ratio of 8, which was higher than the maximum vanadium leaching rate of 90.89% obtained using regular leaching at 80°C for 120 min. Ultrasonic waves broke and dispersed the solid sample because of ultrasonic cavitation, which increased the contact area of the roasted sample and the leaching medium, the solid–liquid mass transfer, and the vanadium leaching rate.

Extraction of Vanadium from Vanadium Slag Via Non-salt Roasting and Ammonium Oxalate Leaching

A clean method featuring non-salt roasting followed by (NH4)2C2O4 leaching to recover vanadium from vanadium slag was proposed. The carcinogenic Cr6+ compounds and exhaust gases were avoided, and the water generated from vanadate precipitation may be recycled and reused in this new leaching process. The leaching residues may be easily used by a blast furnace. Moreover, (NH4)2C2O4 solution was used as a leaching medium to avoid expensive and complicated ammonium controlling operations as a result of the stability of (NH4)2C2O4 at a high temperature. The transformation mechanisms of vanadium- and chromium-bearing phases were systematically investigated by x-ray diffraction analysis and scanning electron microscopy with energy-disperse x-ray spectrometry, respectively. In addition, the effects of oxygen concentration, roasting temperature, and holding time on vanadium recovery were investigated. Finally, the effects of leaching variables on the vanadium leaching rate were also examined.

Closed circuit recovery of copper, lead and iron from electronic waste with citrate solutions

An integral closed circuit hydrometallurgical process is presented for base metal recovery from electronic waste. The leaching medium consists of a sodium citrate solution, from which base metals are retrieved by direct electrowinning, and the barren solution is recycled back to the leaching stage. This leaching-electrowinning cycle was repeated four times. The redox properties of the fresh citrate solution, as well as the leach liquors, were characterized by cyclic voltammetry to determine adequate conditions for metal reduction, as well as to limit citrate degradation. The leaching efficiency of electronic waste, employing the same solution after four complete cycles was 71, 83 and 94% for copper, iron and lead, respectively, compared to the original leach with fresh citrate solution.

Kinetic Aspects of Leaching Zinc from Waste Galvanizing Zinc by Using Hydrochloric Acid Solutions

In this work, the results of acid leaching of flux skimmings coming from two plants are presented. Sample A contained two phases, Zn(OH)Cl and NH4Cl. In sample B, the presence of three phases, Zn5(OH)8Cl2·H2O, (NH4)2(ZnCl4) and ZnCl2(NH3)2, was proved. The aqueous solution of hydrochloric acid and distilled water was used as the leaching medium. The effects of the leaching time, temperature and concentration of the leaching medium on the zinc extraction were investigated. The apparent activation energy, E a = 4.61 kJ mol−1, and apparent reaction order n = 0.18 for sample A, and the values E a = 6.28 kJ mol−1 and n = 0.33 for sample B were experimentally determined. Zinc leaching in acid medium is a diffusion-controlled process.

UTILIZATION OF DRINKING WATER TREATMENT SLUDGE TO PRODUCE ALUMINUM SULFATE

In Egypt, water treatment industry consumes about 365,000 tons of aluminum sulfate as coagulant and produces more than 100 million tons of semidried sludge per year. The common disposal system of alum sludge in Egypt is to discharge it into natural water bodies. Toxic nature of free and complexed aluminum species to aquatic life, stringent environmental regulations on disposal of sludge into water bodies and costs of the chemicals used in water treatment process and sludge treatment led to evaluate coagulant recovery and subsequent reuse. The present work aimed at aluminum metal recovery from sludge obtained from El-Shiekh Zayd water treatment plant by acidification method to produce aluminum sulfate coagulant. Sludge from drying beds was characterized and sulfuric acid was selected as the acidic leaching medium and effect of five variables were tested: acid concentration (N), sludge weight (g), mixing speed (rpm), temperature (oC) and leaching time (min) was studied. Moreover, the process efficiency was evaluated at different operating conditions. Then optimum conditions were applied to get maximum recovery for aluminum sulfate. Maximum recovery is 94.2 % at acid concentration 1.5 N, sludge weight 5 g, mixing speed 60 rpm, temperature 60 oC and leaching time 40 min.

Comparación del potencial oxidativo de Acidithiobacillus ferrooxidans, en un proceso de biodesulfurización de carbón

<p>En este estudio se comparó la actividad oxidativa de dos cepas de Acidithiobacillus ferrooxidans en un proceso de desulfurización, empleando un carbón sub-bituminoso alto en azufre (2.30% de azufre total, con 1.06% pirítico, 1.10% orgánico y 0.14% de sulfatos), proveniente de la mina “La Guacamaya” ubicada en Puerto Libertador–Córdoba, Colombia. Se realizaron ensayos a nivel de erlenmeyer, la concentración de hierro total en la solución fue de 200 mg/L y 1200 mg/L respectivamente, empleando sulfato ferroso. El proceso fue monitoreado mediante mediciones periódicas de los principales factores físico-químicos implicados (pH, potencial de óxido-reducción (Eh), hierro en solución y concentración celular). Según los resultados obtenidos, la mayor eficiencia del proceso se logró, al trabajar con microorganismos compatibles con Acidithiobacillus ferrooxidans y una concentración de sulfato ferroso inicial de 1200 mg/L, el cual obtuvo la mayor tasa de oxidación de pirita (Py oxidada) (68%), así como, mejores condiciones en el medio lixiviante (pH: 1,47; Eh: 625 mV; 6.3×10 8 células/mL) en comparación con el cultivo axénico a las mismas condiciones (Py oxidada: 52%, pH: 1,63, Eh: 580 mV, 5.1×10 8 células/mL), después de 12 días de experimentación.</p>

Effect of Leaching Process for Ceramic Core on Micro-structure and Mechanical Property of Investment Cast Co-base Superalloy DZ40M

Effect of the leaching process of Si O2- and Al2O3-based ceramic core on the microstructure and mechanical property of the investment cast Co-based superalloy DZ40 M is investigated. It is shown that after immersion in the leaching medium for Si O2-based ceramic core for 24 h, the microstructure and mechanical property of the alloy does not vary evidently; although after immersion in the leaching medium for Al2O3-based ceramic core for above 300 h, the microstructure variation of DZ40 M alloy is not evident, but its mechanical property decreased remarkably, which may be due to the occurrence of an embrittled layer of about 1 mm in thickness on the alloy surface. The embrittled layer is caused by hydrogen embrittlement resulted from charging hydrogen during immersion in the leaching medium for Al2O3-based ceramic core.

Leaching behaviour of metals from post-underground coal gasification cavity residues in water differing in mineralization

Abstract The aim of this study was to examine whether water entering the post-reaction area after underground coal gasification (UCG) leaches metals from the post-processing waste in the cavity to such a degree that it can pose a threat to the environment. In the studies, ashes and chars arising from hard coal and lignite gasification have been used. Leaching tests have been performed with the usage of deionized water and two types of mine water that greatly differ in mineralization. The physicochemical composition of the obtained eluates has been analysed. The coefficients of dispersion (distribution), kd, have been estimated, which allowed determination of the mobility of metals under test and thus their ability to leach to the water phase. Metals present in the process of UCG have been described in terms of volatility and divided into three groups. In addition, the concentrations of metals in the eluates, depending on the leaching medium used, have been investigated. It has been found that the majority of tested elements tend to be leached in a stronger degree from ash residues than from chars. In comparison with the residues from hard coal, the residues of gasified lignite show the higher relation to the water phase. The presence of such elements as Cr, Pb or Cd in eluates may suggest that toxic metals are able to leach to water from the residues of the gasification process and a non-negligible risk of environment contamination might occur.