Sequential extraction of metals from mixed and digested sludge from aerobic WWTPs sited in the south of Spain

The content of heavy metals is the major limitation to the application of sewage sludge in soil. However, assessment of the pollution by total metal determination does not reveal the true environmental impact. It is necessary to apply sequential extraction techniques to obtain suitable information about their bioavailability or toxicity. In this paper, sequential extraction of metals from sludge before and after aerobic digestion was applied to sludge from five WWTPs in southern Spain to obtain information about the influence of the digestion treatment in the concentration of the metals. The percentage of each metal as residual, oxidizable, reducible and exchangeable form was calculated. For this purpose, sludge samples were collected from two different points of the plants, namely, sludge from the mixture (primary and secondary sludge) tank (mixed sludge, MS) and the digested-dewatered sludge (final sludge, FS). Heavy metals, Al, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Ti and Zn, were extracted following the sequential extraction scheme proposed by the Standards, Measurements and Testing Programme of the European Commission and determined by inductively-coupled plasma atomic emission spectrometry. The total concentration of heavy metals in the measured sludge samples did not exceed the limits set out by European legislation and were mainly associated with the two less-available fractions (27-28% as oxidizable metal and 44-50% as residual metal). However, metals as Co (64% in MS and 52% in FS samples), Mn (82% in MS and 79% in FS), Ni (32% in MS and 26% in FS) and Zn (79% in MS and 62% in FS) were present at important percentages as available forms. In addition, results showed a clear increase of the concentration of metals after sludge treatment in the proportion of two less-available fractions (oxidizable and residual metal).     

Variations of metal distribution in sewage sludge composting

In the study, the variations of heavy metal distributions (of Cu, Mn, Pb, and Zn) during the sewage sludge composting process were investigated by sequential extraction procedures. The total content of Cu and Zn in the composted mixture increased after the composting process. Mn and Zn were mainly found in mobile fractions (exchangeable fraction (F1), carbonate fraction (F2), and Fe/Mn oxide fraction (F3)). Cu and Pb were strongly associated with the stable fractions (organic matter/sulfides fraction (F4) and residual fraction (F5)). These five metal fractions were used to calculate the metal mobility (bioavailability) in the sewage sludge and composted mixture. The mobility (bioavailability) of Mn, Pb, and Zn (but not Cu) increased during the composting process. The metal mobility in the composted mixture ranked in the following order: Mn>Zn>Pb>Cu.     

A study of heavy metals and their fate in the composting of tannery sludge

Tannery waste is categorized as toxic and hazardous in Malaysia due to its high content of Cr (in excess of 500 mg/kg) and other heavy metals. Heavy metals, when in high enough concentrations, have the potential to be both phytotoxic and zootoxic. Heavy metals are found as contaminants in tannery sludge. This investigation aimed to identify the fate of chromium, cadmium, copper, lead, and zinc concentrations in tannery sludge throughout a 50-day composting cycle. The results of this study showed a general increase in the removal of Cr, Cd, Pb, and to a much smaller extent Zn and Cu, manifested by a decrease in their overall concentrations within the solid fraction of the final product (the decreases were likely the result of leaching). Furthermore, in using a sequential extraction method for sludge composting at different phases of treatment, a large proportion of the heavy metals were found to be associated to the residual fraction (70-80%) and fractions more resistant to extraction, X-NaOH, X-EDTA, X-HNO3 (12-29%). Less than 2% of the metals were bound to bioavailable fractions X-(KNO3+H2O).     

Waste paper and clinoptilolite as a bulking material with dewatered anaerobically stabilized primary sewage sludge (DASPSS) for compost production

Environmental problems associated with sewage sludge disposal have prompted strict legislative actions over the past few years. At the same time, the upgrading and expansion of wastewater treatment plants have greatly increased the volume of sludge generated. The major limitation of land application of sewage sludge compost is the potential for high heavy metal content in relation to the metal content of the original sludge. Composting of sewage sludge with natural zeolite (clinoptilolite) can enhance its quality and suitability for agricultural use. However, the dewatered anaerobically stabilized primary sewage sludge (DASPSS) contained a low concentration of humic substances (almost 2%), and the addition of the waste paper was necessary in order to produce a good soil conditioner with high concentrations of humics. The final results showed that the compost produced from DASPSS and 40-50% w/w of waste paper was a good soil fertilizer. Finally, in order to estimate the metal leachability of the final compost product, the generalized acid neutralization Capacity (GANC) procedure was used, and it was found that by increasing the leachate pH, the heavy metal concentration decreased. The application of the sequential chemical extraction indicated that metals were bound to the residual fraction characterized as a stabilize fractions.     

Accumulation and fate of selected heavy metals in a biological wastewater treatment system

The aim of this research was to study the accumulation and removal of heavy metals (Cd, Cu, Pb, Zn) by a biological wastewater treatment system. Heavy metal contents in the influent and effluent wastewater were compared. Also, the heavy metal contents in the sludge before and after anaerobic digestion were compared. The results showed: (1) more pronounced variations in the contents of Cu and Zn than that of Cd and Pb, which showed that at 0.02 for Cd and 0.05 mg/l for Pb, the reduction in their contents was insignificant; (2) that removal of heavy metals was directly proportional to their initial contents in the influent wastewater. Corresponding to the influent contents, in increasing order, the reduction in heavy metal contents was: Cd相似文献   

Heavy metal removal from contaminated sludge for land application: a review

In recent years, various methods for heavy metal removal from sewage sludge have been extensively studied in order to minimize the prospective health risks of sludge during land application. In this paper, a comparative review and critical analysis of the application of chemical extraction, bioleaching, electroreclamation, and supercritical fluid extraction (SFE), in removing heavy metals from contaminated sludges is presented. Moreover, speciation studies, which can indicate ease of leachability of the different forms of heavy metals in sludge, are also presented. Experimental studies revealed a broad range in metal extraction efficiencies of the different extraction technologies. Acid treatment seemed to effectively remove Cd, attaining as much as 100% removal for some studies, as compared to bioleaching. SFE also gave higher removal efficiency than bioleaching. Cr, Pb and Ni seemed to be also effectively removed by the acid treatment. For the removal of Cu, Mn and Zn, the bioleaching process seemed to be appropriate with maximum removal efficiencies of 91%, 93% and 96% for the three metals, respectively, and as high as 64% minimum removal efficiency for Zn. The SFE process also gave good results for Cu, Mn and Zn removal. Electroreclamation exhibited better removal efficiency for Mn, but is still inferior to acid treatment and bioleaching processes. For chemical extraction, because of the adverse impacts that can result from the use of inorganic acids and complexing agents, interest can be directed more toward utilizing organic acids as extracting agents because of their biodegradability and capability to remove metals at mildly acidic condition, hence requiring less acid. The bioleaching process, although it seems to give a higher yield of metal extraction with lower chemical cost than chemical extraction, may be limited by the inability of the system to cope with the natural environmental conditions, requires strict monitoring of aeration rate and temperature and has applicability to only low sludge solids concentration. A full-scale study would be useful to better assess the efficiency of the process. The electroreclamation technology is limited by its relatively higher energy consumption and limited applicability to sludge. The SFE method, on the other hand, is limited by the complexity of the process and the cost of ligands suitable for effective metal extraction. Both of these technologies are still in their early stage of application and hence there is a need for further basic and applied studies. Finally, the common advantage for almost all treatment technologies studied is that the extraction efficiencies for some metals are high enough to remove metals from sludge to levels suitable for land application.     

Characteristic of heavy metals in biochar derived from sewage sludge

This study investigates the characteristic of heavy metals (Pb, Zn, Cu, Cd, Cr, Ni and As) in biochar derived from sewage sludge at different pyrolysis temperatures (300, 400, 500, 600 and 700 °C). The heavy metal concentrations, chemical speciation distribution, leaching toxicity, and bio-available contents were investigated using ICP-OES after microwave digestion, a sequential extraction procedure recommended by the Community Bureau of Reference (BCR), an improved nitric acid–sulphuric acid method, and diethylenetriamine pentaacetic acid (DTPA) extraction method, respectively. The results showed that a great percentage of the heavy metals remained in biochar, the concentrations of heavy metals in biochar (except Cd in B7) were higher than that in sludge, and the enrichment of the heavy metals in biochar enhanced with the pyrolysis temperature. Although the effect of pyrolysis temperature on the chemical speciation distribution, the leaching toxicity and the bio-available contents of heavy metals in biochar was inconsistent, the potential risk of biochar on soil and groundwater contamination was lower than sewage sludge.     

Fixation and partitioning of heavy metals in slag after incineration of sewage sludge

Fixation of heavy metals in the slag produced during incineration of sewage sludge will reduce emission of the metals to the atmosphere and make the incineration process more environmentally friendly. The effects of incineration conditions (incineration temperature 500-1100°C, furnace residence time 0-60min, mass fraction of water in the sludge 0-75%) on the fixation rates and species partitioning of Cd, Pb, Cr, Cu, Zn, Mn and Ni in slag were investigated. When the incineration temperature was increased from 500 to 1100°C, the fixation rate of Cd decreased from 87% to 49%, while the fixation rates of Cu and Mn were stable. The maximum fixation rates for Pb and Zn and for Ni and Cr were reached at 900 and 1100°C, respectively. The fixation rates of Cu, Ni, Cd, Cr and Zn decreased as the residence time increased. With a 20min residence time, the fixation rates of Pb and Mn were low. The maximum fixation rates of Ni, Mn, Zn, Cu and Cr were achieved when the mass fraction of water in the sludge was 55%. The fixation rate of Cd decreased as the water mass fraction increased, while the fixation rate of Pb increased. Partitioning analysis of the metals contained in the slag showed that increasing the incineration temperature and residence time promoted complete oxidation of the metals. This reduced the non-residual fractions of the metals, which would lower the bioavailability of the metals. The mass fraction of water in the sludge had little effect on the partitioning of the metals. Correlation analysis indicated that the fixation rates of heavy metals in the sludge and the forms of heavy metals in the incinerator slag could be controlled by optimization of the incineration conditions. These results show how the bioavailability of the metals can be reduced for environmentally friendly disposal of the incinerator slag.     

分步沉淀法处理酸性矿山废水

采用分步沉淀工艺处理酸性矿山废水,考察了工艺条件对废水中有价金属元素回收效果的影响。实验结果表明:Ca(OH)_2为适宜的废水pH调节剂;调节废水pH至4.00左右并投加0.05 mL/L的H_2O_2,可首先去除Fe~(2+)及Fe~(3+),得到富Fe渣(w(Fe)=51.00%);调节废水pH至6.00~6.50,先投加50 mg/L的Na_2S,去除废水中的Cu~(2+),获得富Cu渣(w(Cu)=10.89%),再将Na_2S的投加量增至100 mg/L,去除废水中的Zn与Mn,获得富Zn-Mn渣(w(Cu)=2.37%,w(Mn)=6.79%,w(Pb)=1.61%);进一步调节废水pH至8.40,可去除剩余的Zn、Mn及其他重金属。分步沉淀工艺处理后的废水可达标排放,产生的富Fe渣、富Cu渣及富Zn-Mn渣可直接出售或具有利用价值。分步沉淀工艺可实现有价金属元素的高效回收,大幅度降低废水处理的实际成本,值得工程应用与推广。     

Solubility and Potential Mobility of Heavy Metals in Two Contaminated Urban Soils from Stockholm,Sweden

The solubility and potential mobility of heavy metals (Cd, Cu,Hg, Pb and Zn) in two urban soils were studied by sequential andleaching extractions (rainwater). Compared to rural (arable) soils on similar parent material, the urban soils were highlycontaminated with Hg and Pb and to a lesser extent also with Cd,Cu and Zn. Metal concentrations in rainwater leachates were related to sequential extractions and metal levels reported fromStockholm groundwater. Cadmium and Zn in the soils were mainly recovered in easily extractable fractions, whereas Cu and Pb were complex bound. Concentrations of Pb in the residual fractionwere between two- and eightfold those in arable soils, indicatingthat the sequential extraction scheme did not reflect the solidphases affected by anthropogenic inputs. Cadmium and Zn conc. inthe rainwater leachates were within the range detected in Stockholm groundwater, while Cu and Pb conc. were higher, whichsuggests that Cu and Pb released from the surface soil were immobilised in deeper soil layers. In a soil highly contaminatedwith Hg, the Hg conc. in the leachate was above the median concentration, but still 50 times lower than the max concentration found in groundwater, indicating the possibilityof other sources. In conclusion, it proved difficult to quantitatively predict the mobility of metals in soils by sequential extractions.     

Heavy metal mobility and potential availability in animal manure: using a sequential extraction procedure

In this study, dairy cow manure, goat manure, and chicken manure were collected from three farms and analyzed to find out the concentration of Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. The concentration and potential of mobility and availability of heavy metals were studied in the animal manure samples. BCR Sequential extraction procedure was used to determine the binding forms of the metals. In this study, pseudo total concentrations of Mn and Zn were found out to be predominant in all the types of animal manure samples. According to the results, it was traced that Cr, Cu, and Ni were observed to be at the second highest level while Cd, Co, and Pb were seen at the lowest level in all the manure samples. When extractable amounts of heavy metals are taken into consideration, it is seen that the amount of the mobile fractions of heavy metals except for Cr and Ni are higher in comparison with that of immobile fraction in all the animal manure samples. It was also viewed that Mn, Cd, and Zn are more available in dairy cow manure and chicken manure whereas Cd, Co, and Mn are more available in goat manure.     

Extractability and leachability of heavy metals in Technosols prepared from mixtures of unconsolidated wastes

Mixtures of wastes were prepared to improve on the characteristics of the individual ingredients as Technosols, with special attention given to heavy metal extractability. An anaerobic digested sewage sludge and a CaO-treated aerobic sludge were used. A mixture of the two sludges (50:50 DW basis) was also prepared to provide a third type of sludge. The residues were mixed with other types of waste, such as fly ash, Linz-Donowitz slag, foundry sand, shot blasting machine scrap, fettling and barley straw. Extractability of Cu, Cr, Ni, and Zn by 0.01 M CaCl(2) extraction (Me(CACI(2)) was carried out, and leachability of these elements was estimated by acidification of an aqueous suspension of the mixtures with 0.5 N acetic acid (Me(acetic)). The total concentrations of the metals were also determined (Me(T)). The Me(CACI(2)/Me(T) ratios for Cu and Ni (means: 4.0% and 3.1%) were higher than those for Cr and Zn (means: 0.07% each). The mean Me(acetic)/Me(T) ratios followed the order Ni, Zn, Cu, and Cr (19.5%, 4.1%, 3.7%, and 0.09%, respectively). The results highlight the existence of complex interactions among organic matter solubility, pH and heavy metal extractability.     

Effects of cement on redistribution of trace metals and dissolution of organics in sewage sludge and its inorganic waste-amended products

The suitability of using cement-stabilized sludge products as artificial soils in earth works was evaluated. The sludge products investigated were cemented sludge, cement-treated clay-amended sludge (SS+MC), and cement-treated copper slag-amended sludge (SS+CS). The leachability of lead (Pb), zinc (Zn), copper (Cu), and chromium (Cr) were assessed using the sequential extraction technique, toxicity characteristic leaching procedure (TCLP), NEN 7341 availability test, and column leaching test. The results indicated that Zn leachability was reduced in all the cement-stabilized sludge products. In contrast, Cu was transferred from the organic fraction to the readily leachable phases in the cement-stabilized sludge products and therefore exhibited increased leachability. The increased Cu leachability could be attributed to dissolution of humic substances in the sludge as a result of elevated pH. Good correlation between dissolved organic carbon (DOC) and heavy metal leaching from the cement-stabilized sludge products was observed in the column leaching experiment. Even with a cement percentage as small as 12.5%, calcium silicate hydrate (C-S-H) was formed in the SS+MC and SS+CS products. Inclusion of the marine clay in the SS+MC products could reduce the leaching potentials of Zn, and this was the great advantage of the marine clay over the copper slag for sludge amendment.     

Characterization of a thermal power plant air heater washing waste: a case study from Iran.

In Iran most of the electricity is generated by thermal power plants. As a result of fuel oil burning in winter time, the air heaters of the boilers have to be washed and cleaned frequently. The wastewater originating from air heater washing is then treated in an effluent treatment plant by chemical precipitation followed by dewatering of the sludge produced. The resulting waste is classified as specific industrial waste that should be characterized in detail under the Waste Management Act of Iran. The quantity of this waste produced in the studied power plant is about 20 tonnes year(-1). In the present investigation, the first to be carried out in Iran, seven composite samples of dewatered sludge from air heater washing wastewater treatment were subjected to investigation of the physical properties, chemical composition and leaching properties. The most likely pollutants that were of concern in this study were heavy and other hazardous metals (Cd, Co, Cr, Mn, Ni, Pb, Zn and V). The results revealed that mean pH, wet and dry density and moisture content of the waste were 6.31, 1532 kg m(-30, 1879 kg m(-3) and 15.35%, respectively. Magnetite, SiO2, P2O5, CaO, Al2O3 and MgO were the main constituents of the waste with a weight percentage order of 68.88, 5.91, 3.39, 2.64, 2.59 and 1.76%, respectively. The toxicity characteristic leaching procedure test results for some heavy and other hazardous metals showed that mean elemental concentrations of Cd, Co, Cr, Mn, Ni, Pb, V and Zn in leachate were 0.06, 1.55, 5.49, 36.32, 209.10, 0.58, 314.06 and 24.84 mg L(-1), respectively. According to the Waste Management Act of Iran this waste should be classified as hazardous and should be disposed of in accordance with hazardous waste disposal regulations.     

Influence of calcium chloride on the thermal behavior of heavy and alkali metals in sewage sludge incineration

In order to separate and reuse heavy and alkali metals from flue gas during sewage sludge incineration, experiments were carried out in a pilot incinerator. The experimental results show that most of the heavy and alkali metals form condensed phase at temperature above 600 degrees C. With the addition of 5% calcium chloride into sewage sludge, the gas/solid transformation temperature of part of the metals (As, Cu, Mg and Na) is evidently decreased due to the formation of chloride, while calcium chloride seems to have no significant influence on Zn and P. Moreover, the mass fractions of some heavy and alkali metals in the collected fly ash are relatively high. For example, the mass fractions for Pb and Cu in the fly ash collected by the filter are 1.19% and 19.7%, respectively, which are well above those in lead and copper ores. In the case of adding 5% calcium chloride, the heavy and alkali metals can be divided into three groups based on their conversion temperature: Group A that includes Na, Zn, K, Mg and P, which are converted into condensed phase above 600 degrees C; Group B that includes Pb and Cu which solidify when the temperature is above 400 degrees C; and Group C that includes As, whose condensation temperature is as low as 300 degrees C.     

Comparison of leaching characteristics of heavy metals in APC residue from an MSW incinerator using various extraction methods

This study investigates four extraction methods (water extraction, toxicity characteristics leaching procedure (TCLP), modified TCLP with pH control, and sequential chemical extraction (SCE)), each representing different liquid-to-solid (L/S) ratios, pH controls, and types of leachant, and their effects on the leaching concentration of heavy metals in municipal solid waste (MSW) incinerator air pollution control (APC) residue. The results indicated that for extraction with distilled water, the heavy metal leaching concentration (mg/l) decreased with L/S ratio, but the amount of heavy metal released (AHMR), defined as the leached amount of heavy metals to the weight of the tested sample (mg/kg), increased with an increase in L/S ratio, in the range of 2-100. The results also showed that both the leaching concentration and the amount of released metals were strongly pH-dependent in the TCLP and modified TCLP tests. In the case of pHs lower than 6.5, the leaching concentrations of Cd, Pb, Cu, Zn, and Cr decreased with an increase in pH. As pH increased higher than 6.5, Cr and Zn were almost insoluble. Meanwhile, Cd and Cu also showed a similar trend but at pHs of 8.5 and 7.5, respectively. Due to the nature of amphoteric elements, in the case of pHs higher than 7, the Pb leaching concentration increased with increasing pH. In modified TCLP tests with the pH value controlled at the same level as in the SCE test, the heavy metal speciation approached the extractable carbonate bound fraction by the SCE. Both amounts of targeted metals leached from the SCE and modified TCLP tests were much higher than those for the regular TCLP and water extraction tests.     

Effect of composting process on phytotoxicity and speciation of copper, zinc and lead in sewage sludge and swine manure

The concentration and bioavailability of heavy metals in composted organic wastes have negative environmental impacts following land application. Aerobic composting procedures were conducted to investigate the influences of selected parameters on heavy metal speciation and phytotoxicity. Results showed that both of sewage sludge (SSC) and swine manure (SMC) composting systems decreased the pH, the content of organic matter (OM) and dissolved organic carbon (DOC), and total amounts of Cu, Zn and Pb. Sequential extraction showed that readily extractible fractions of exchangeable and carbonate in Cu and Zn increased during SSC composting but decreased during SMC composting, thus their bioavailability factors (BF) enhanced in SSC but declined in SMC. The fraction of reducible iron and manganese (FeMnOX) of Cu and Zn in SSC and FeMnOX-Cu in SMC decreased, but FeMnOX-Zn in SMC gradually increased in the process of compost. In contrast, the changes of Pb distributions were similar in two organic wastes. Pb was preferentially bound to the residual fraction and its BF decreased. The evolution of heavy metal distributions and BF depended on not only total metal concentrations but also the other properties, such as pH, decomposition of OM and decline of DOC. The germination rate (RSG), root growth (RRG) and germination index (GI) of pakchoi (Brassica Chinensis L.) increased during the composting process. Linear regression analysis demonstrated that GI, which could represent phytotoxic behavior to the plants, could be poorly predicted by BF or total amount of metals, i.e., BF-Zn, T-Cu. However, the inclusion of other physicochemical parameters (pH, OM and DOC) could enhance the linear regression significances (R).     

Leachability and metal-binding capacity in ageing landfill material

In order to study the stability of landfilled heavy metals, landfill material from a combined household and industrial waste landfill was aerated for 14 months to simulate the natural ageing processes as air slowly begins to penetrate the landfill mass. During aeration, the pH of the landfill material decreased from around 8.6 to 8.1 and the carbon content also decreased. In order to investigate the possible fate of metals in ageing landfills, a four-stage sequential extraction technique was applied. The ability of the materials to bind metal ions by electrostatic attractions and to form stronger complexes was studied separately. The amount of exchangeable cations, the capacity to bind metal ions by electrostatic attraction and the capacity of the landfill material to complex copper ions were increased by the aeration process. However, results from the sequential analysis showed an increased solubility of sulphur and some metals (Cd, Co, Cu, Ni and Zn). Equilibrium speciation models (Medusa) indicated that the organic matter deposit had a significant capacity to bind metal ions provided that pH was sufficiently high. However, as carbonates are consumed over time, the risk for metal mobility increases. Therefore, the landfills can become an environmental risk, depending on variations in the solubility of metal ions due to changes in pH, redox status and the availability of organic material.     

Removal of mixed contaminants by Fe0-based biobarrier in flow-through columns using recycled waste materials

The present study investigated the reactivity and ability of permeable reactive barriers [zero-valent iron (ZVI)-barrier plus biobarrier) to remove various contaminants (Cd, As, Zn, Cu, Mn, Cr, NO₃ ⁻, NH₄ ⁺, and COD_cr) from synthetic leachate. Two different reactive materials were used in this study, namely ZVI and autoclaved lightweight concrete (ALC). After 90 days of column operation, the contaminant profiles were determined along the length of the columns. The heavy metals were extensively removed in the bio-ALC and sequential barriers (ZVI plus bio-ALC), however the removal efficiencies for the heavy metals Zn and Cr in the ALC and bio-ALC barriers were comparatively low. Nitrate was completely removed (>99.9%) in the ALC, bio-ALC, and sequential barriers. More than 50% of the produced ammonium and organic materials were removed in the biologically reactive zone of the sequential barriers. The results of the present study suggest that sequential barriers are one of the best solutions for in situ remediation and that they can be applied to clean up the leachate released from landfills.     

The storage of sewage sludge: influence of liming on the evolution of copper chemical fractions

Sewage sludge re-used in agriculture has to be stabilized and is often stored for several months before land spreading. Stabilization treatment may affect the behaviour of heavy metals such as Cu, which is an element potentially toxic to the environment. In the present study, the chemical forms of copper have been investigated in heaps of limed and unlimed sludge coming from the wastewater treatment plant of Roselies (Belgium). These limed and unlimed aerobically digested sludges were stored during 4 mo in controlled conditions close to field ones. The sequential extraction procedure developed by Tessier was used to determine the copper chemical forms of representative samples taken in the outer shell and in the depth of the heaps. The physico-chemical properties (pH, organic matter, dry matter and temperature) of these samples were also monitored. This study shows that liming transforms part of organically-bound copper into both exchangeable and residual copper. These changes mainly occur during the first 2 wk of storage. After several months of storage, copper passes from the residual fraction to the exchangeable and oxide fractions. During the whole experiment, changes occur faster in the outer shell than in the depth of the heaps. Thus, we demonstrate that the distribution of the copper forms depends on the storage time and it is different in the outer shell from that in the depth of the heaps.