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.     

Copper,zinc, and nickel recovery from printed circuit boards using an ammonia–ammonium sulphate system

Journal of Material Cycles and Waste Management - The ammoniacal leaching has been considered very selective for copper compared with other leaching systems; however, there are interactions with...     

Electrodeposition of rare-earth elements from neodymium magnets using molten salt electrolysis

Rare-earth element is an important target for recycling in Japan. In our previous work, we demonstrated the selective leaching of rare-earth elements from waste neodymium magnets using chloride molten salt electrolysis. In this study, we investigated the electrodeposition of rare-earth elements using liquid metal as a cathode. The reduction potential obtained using a liquid-zinc electrode was higher than that obtained using a solid molybdenum electrode. A zinc–rare-earth alloy was formed as the electrodeposit. The total rare-earth element content of the electrodeposit was more than 99.8 mass% without zinc and other composition of electrolysis. The activity of rare-earth elements decreased upon alloy formation, suggesting that the oxidation rate of electrodeposited alloy will be decreased.     

Treatment of electronic waste to recover metal values using thermal plasma coupled with acid leaching--a response surface modeling approach

The global crisis of the hazardous electronic waste (E-waste) is on the rise due to increasing usage and disposal of electronic devices. A process was developed to treat E-waste in an environmentally benign process. The process consisted of thermal plasma treatment followed by recovery of metal values through mineral acid leaching. In the thermal process, the E-waste was melted to recover the metal values as a metallic mixture. The metallic mixture was subjected to acid leaching in presence of depolarizer. The leached liquor mainly contained copper as the other elements like Al and Fe were mostly in alloy form as per the XRD and phase diagram studies. Response surface model was used to optimize the conditions for leaching. More than 90% leaching efficiency at room temperature was observed for Cu, Ni and Co with HCl as the solvent, whereas Fe and Al showed less than 40% efficiency.     

Hydrometallurgical recycling of cobalt from zinc plants residue

A large amount of hot filter cake (HFC) is annually generated in Iranian zinc plants. It contains 1% zinc, 16–30% manganese, 5–25% calcium and 1–4.5% cobalt. Usually, zinc is selectively leached by an alkaline medium and its residue is known as alkaline leached HFC (ALHFC). In the present study, the possibility of cobalt extraction from ALHFC was investigated using a creative hydrometallurgical process. At the first stage, zinc and cadmium were selectively removed with sulfuric acid. At the second stage, it was deeply focused on the possibility of selective reductive leaching of cobalt by H₂O₂ as a reductant in the presence of manganese. As results, several differences were found between the mechanism of cobalt and manganese leaching. Accordingly, cobalt leaching was more affected by acid concentration and manganese leaching was more affected by reductant concentration. Consequently, with manipulating these important parameters, it was made possible to selectively separate cobalt from manganese. Based on the obtained results, 90.9% of cobalt and only 10.04% of manganese were leached with 1% of H₂O₂. At the third stage, pregnant cobalt solution was successfully purified through a solvent extraction process with D2EHPA. Finally, cobalt hydroxide as our final product with a purity of more than 99% was precipitated from the pure pregnant solution at 70 °C.     

Long-term leaching test of incinerator bottom ash: evaluation of Cu partition

Two types of leaching tests were performed on the bottom ash from municipal solid waste incinerators. A short-term batch test specified by the America Nuclear Society (ANS) and long-term column tests with acetic acid (pH 5.2) as leaching solution were used to evaluate copper leachability. The Cu leaching after the 5-d ANS test is about 1% of the original Cu content of 5300 mg/kg. Upon addition of a stabilizing agent, the Cu leaching quantity is reduced; the extent of reduction depends on the type of chemical used (phosphate, carbonate and sulfide). The 1.6% Na(2)S addition showed negligible Cu leaching, and Na(2)S was, therefore, used in subsequent column tests. The 30-d column test indicates a steady increase of Cu leaching amount with time and reaches about 1.5% of the original Cu content after 30 d. A 180-d column test further increased the Cu leaching to about 5.1% of the original Cu content, whereas no appreciable Cu leaching was found with the addition of 1.6% Na(2)S. A sequential extraction was conducted on the raw ash, ash with the addition of Na(2)S and the residue ash after 30 d of operation to characterize Cu affinity for different solid fractions. The data were used to evaluate the fate of Cu through these interactions.     

离子液体对废旧印刷线路板中铜、锌、铅的浸出规律

以离子液体1-丁基磺酸-3-甲基咪唑三氟甲烷磺酸盐([BSO_3HMIm]OTf)为浸出剂,初步研究了WPCBs浸铜过程中锌和铅浸出率的影响因素。实验结果表明:铜、锌的浸出率随着WPCBs粒径的减小、H_2O_2溶液加入量的增大而增大,铜的浸出率随浸出温度的升高先增大后减小,锌的浸出率受浸出温度影响不大;铅的浸出率受5种因素影响不大,且总体处于较低水平。在WPCBs粒径为0.100~0.250 mm、离子液体加入量为60.0%(φ)、H_2O_2溶液加入量为7.5%(φ)、固液比为1∶15、浸出温度为50℃的条件下,铜、锌、铅的浸出率分别为99.84%,93.25%,22.46%。     

Experimental and numerical analysis of metal leaching from fly ash-amended highway bases

A study was conducted to evaluate the leaching potential of unpaved road materials (URM) mixed with lime activated high carbon fly ashes and to evaluate groundwater impacts of barium, boron, copper, and zinc leaching. This objective was met by a combination of batch water leach tests, column leach tests, and computer modeling. The laboratory tests were conducted on soil alone, fly ash alone, and URM-fly ash-lime kiln dust mixtures. The results indicated that an increase in fly ash and lime content has significant effects on leaching behavior of heavy metals from URM-fly ash mixture. An increase in fly ash content and a decrease in lime content promoted leaching of Ba, B and Cu whereas Zn leaching was primarily affected by the fly ash content. Numerically predicted field metal concentrations were significantly lower than the peak metal concentrations obtained in laboratory column leach tests, and field concentrations decreased with time and distance due to dispersion in soil vadose zone.     

氨浸出含锌烟尘制取活性氧化锌

采用氨浸出法处理含锌烟尘,浸出液在微波-超声波联合作用下蒸氨得碱式碳酸锌沉淀,再经煅烧制得活性氧化锌.实验结果表明:在总氨浓度为9.0 mol/L、浸出温度为40 ℃、浸出液初始pH为 11.0～11.5、搅拌转速为400 r/min、浸出剂体积与含锌烟尘质量比为4、浸出时间为60 min的浸出条件下,锌的浸出率为83.3%.浸出液经过两段净化除杂后,在超声波功率50 W、微波辐射(微波功率随温度的设定而自动变化)的联合作用下,使溶液体系恒温90 ℃,进行蒸氨,沉淀得到前驱体碱式碳酸锌,经煅烧,得到平均直径为0.4 μm、晶型为六方晶系、片状的活性氧化锌.     

Recovery of copper and cobalt from ancient slag.

About 2.5 million tonnes of copper smelter slag are available in Küre, northern part of Turkey. This slag contains large amounts of metallic values such as copper and cobalt. A representative slag sample containing 0.98% Cu, 0.49% Co and 51.47% Fe was used in the experimental studies. Two different methods, direct acid leaching and acid baking followed by hot water leaching were used for recovering Cu and Co from the slag. The effects of leaching time, temperature and acid concentration on Cu- and Co-dissolving efficiencies were investigated in the direct acid leaching tests. The optimum leaching conditions were found to be a leaching time of 2 h, acid concentration of 120 g L(-1), and temperature of 60 degrees C. Under these conditions, 78% Cu and 90% Co were extracted. In the acid baking + hot water leaching tests, 74% Co was dissolved after 1 h of roasting at 200 degrees C using a 3:1 acid:slag ratio, whereas the Cu-dissolving efficiency was 79% and the total slag weight loss was approximately 50%.     

Dynamics of copper and zinc sedimentation in a lagooning system receiving landfill leachate

This study characterises the sediment dredged from a lagooning system composed of a settling pond and three lagoons that receive leachates from a municipal solid waste (MSW) landfill in France. Organic carbon, carbonate, iron oxyhydroxides, copper (Cu) and zinc (Zn) concentrations were measured in the sediment collected from upstream to downstream in the lagooning system. In order to complete our investigation of sedimentation mechanisms, leachates were sampled in both dry (spring) and wet (winter) seasonal conditions. Precipitation of calcite and amorphous Fe-oxyhydroxides and sedimentation of organic matter occurred in the settling pond. Since different distributions of Zn and Cu concentrations are measured in sediment samples collected downstream in the lagooning system, it is suggested that these elements were not distributed in a similar way in the leachate fractions during the first stage of treatment in the settling pond, so that their sedimentation dynamics in the lagooning system differ. In the lagoons, it was found that organic carbon plays a major role in Cu and Zn mobility and trapping. The presence of macrophytes along the edges provided an input of organic matter that enhanced Cu and Zn scavenging. This edge effect resulted in a two-fold increase in Cu and Zn concentrations in the sediment deposited near the banks of the lagoons, thus confirming the importance of vegetation for the retention of Cu and Zn in lagooning systems.     

Leachability of municipal solid waste ashes in simulated landfill conditions

In Japan the volume of municipal solid waste is reduced by incineration, with fly ash and bottom ash disposed in controlled landfills. The leachability of anions and heavy metal cations, Zn, Cu and Pb, from MSW fly ash and bottom ash at different pHs was examined using batch- and column-leaching tests. The MSW ashes had a high capacity for neutralizing acids. Behaviour during leaching depended on the pH of the solution. For the volumes applied, the leachabilities of MSW fly ash were very similar at pHs from 3 to 6. Due to its amphoteric nature, Pb is leachable at pHs of approximately 10 or more, with leachate concentrations of about 3 and 3-10mg/L for the fly ash and bottom ash, respectively, much higher than for Zn and Cu. Pb concentrations for most leaching solutions were 1 and 3mg/L for the fly ash and bottom ash, respectively. Zn, and Cu leached at low concentrations for solutions of pH 3-6. Na and K ions leached at high concentrations of approximately 5000 mg/L in the first batch leaching test, decreasing to 10mg/L by the fourth leach. Ca and Mg ions leached more gradually than Na and K. Cl(-) and SO(4)(2+) ions were the major anions in the MSW ash. The high pH and cation leaching are expected to have negative impacts on the performance of clay liners.     

Chemical properties of heavy metals in typical hospital waste incinerator ashes in China

Incineration has become the main mechanism for hospital waste (HW) disposal in China after the outbreak of Severe Acute Respiratory Syndrome (SARS) in 2003. However, little information is available on the chemical properties of the resulting ashes. In the present study, 22HW ash samples, including 14 samples of bottom ash and eight samples of fly ash, were collected from four typical HW incineration plants located across China. Chemical analysis indicated that the HW ashes contained large amounts of metal salts of Al, Ca, Fe, K, Mg, Na with a concentration range of 1.8-315gkg(-1). Furthermore, the ashes contained high concentrations of heavy metals such as Ag, As, Ba, Bi, Cd, Cr, Cu, Mn, Ni, Pb, Ti, Sb, Sn, Sr, Zn with a vast range of 1.1-121,411mgkg(-1), with higher concentrations found in the fly ash samples. Sequential extraction results showed that Ba, Cr, Ni and Sn are present in the residual fraction, while Cd existed in the exchangeable and carbonate fractions. As, Mn, Zn existed in the Fe-Mn oxide fraction, Pb was present in the Fe-Mn oxide and residual fractions, and Cu was present in the organic matter fraction. Furthermore, toxicity characteristic leaching procedure (TCLP) results indicated that leached amounts of Cd, Cu and Pb from almost all fly ash samples exceeded the USEPA regulated levels. A comparison between the HW ashes and municipal solid waste (MSW) ash showed that both HW bottom ash and fly ash contained higher concentrations of Ag, As, Bi, Cd, Cr, Cu, Pb, Ti, and Zn. This research provides critical information for appropriate HW incineration ash management plans.     

Evaluation of gold and silver leaching from printed circuit board of cellphones

Electronic waste has been increasing proportionally with the technology. So, nowadays, it is necessary to consider the useful life, recycling, and final disposal of these equipment. Metals, such as Au, Ag, Cu, Sn and Ni can be found in the printed circuit boards (PCB). According to this, the aims of this work is to characterize the PCBs of mobile phones with aqua regia; obtaining “reference” values of leaching, to gold and silver, with cyanide and nitric acid, respectively; and study the process of leaching of these metals in alternative leaching with sodium thiosulfate and ammonium thiosulfate. The metals were characterized by digesting the sample with aqua regia for 1 and 2 h at 60 °C and 80 °C. The leaching of Au with a commercial reagent (cyanide) and the Ag with HNO₃were made. The leaching of Au and Ag with alternative reagents: Na₂S₂O_3, and (NH₄)₂S₂O₃ in 0.1 M concentration with the addition of CuSO₄, NH₄OH, and H₂O₂, was also studied. The results show that the digestion with aqua regia was efficient to characterize the metals present in the PCBs of mobile phones. However, the best method to solubilize silver was by digesting the sample with nitric acid. The leaching process using sodium thiosulfate was more efficient when an additional concentration of 0.015 and 0.030 M of the CuSO₄ was added.     

Physical containment of municipal solid waste incineration bottom ash by accelerated carbonation

Accelerated carbonation of municipal solid waste incineration residues is effective for immobilizing heavy metals. In this study, the contribution of the physical containment by carbonation to immobilization of some heavy metals was examined by some leaching tests and SEM–EDS analysis of untreated, carbonated, and milled bottom ash after carbonation that was crushed with a mortar to a mean particle size of approximately 1 μm. The surface of carbonated bottom ash particles on SEM images seemed mostly coated, while there were uneven micro-spaces on the surface of the untreated bottom ash. Results of Japan Leaching Test No. 18 (JLT18) for soil pollution showed that milling carbonated bottom ash increased the pH and EC. The leaching concentration of each element tended to be high for untreated samples, and was decreased by carbonation. However, after the milling of carbonated samples, the leaching concentration became high again. The immobilization effect of each element was weakened by milling. The ratio of physical containment effect to immobilization effects by accelerated carbonation was calculated using the results of JLT18. The ratio for each element was as follows: Pb: 13.9–69.0 %, Cu: 12.0–49.1 %, Cr: 24.1–99.7 %, Zn: 20.0–33.3 %, and Ca: 28.9–63.4 %.     

The influence of pH on the leaching behaviour of inorganic components from municipal solid waste APC residues

The influence of pH on the leaching behaviour of air pollution control (APC) residues produced in municipal solid waste incineration (MSWI) is addressed in this study. The residue is considered hazardous waste, and in accordance with their chemical properties, the leaching of contaminants into the environment is the main concern. Several leaching tests can be used for research studies or regulatory purposes, where a wide variety of conditions may be tested. Our work deals mainly with the leaching behaviour of toxic heavy metals (Pb, Cd, Zn, Cr, Ni, Cu) and inorganics associated with soluble salts (Na, K, Ca, Cl). The main goal is to obtain an overview of the leachability of APC residues produced in a Portuguese MSWI process. Among the different variables that may have influence on the leaching behaviour, pH of the leachant solution is the most important one, and was evaluated through pH static tests. The acid neutralization capacity (ANC) of the residue was also determined, which is in the range of 6.2–6.8 meq g^?1 (for pH = 7) and 10.1–11.6 meq g^?1 (for pH = 4). The analysis of the leaching behaviour is particularly important when the leaching is solubility controlled. The amphoteric behaviour of some elements was observed, namely for Pb and Zn, which is characterized through high solubilization at low and high pH and moderate or low solubility at neutral or moderate high pH. The solubility curves for Pb, Cd, Zn, Cr, Ni and Cu as a function of pH were obtained, which are very useful for predicting the leaching behaviour in different scenarios. The solubility of K and Na reveals to be nearly independent of the solution pH and the released amount is mainly availability-controlled. Moreover, the pH static test showed that Cl^? is the most pH-independent species. The APC residue turns out to be a hazardous waste because of the high leaching of lead and chloride. On the other hand, leaching of elements like cadmium, nickel and copper is limited by the high pH of the residue, and as long as the waste keeps its ANC, the risk of mobilization of these elements is low.     

Process development for recovery of copper and precious metals from waste printed circuit boards with emphasize on palladium and gold leaching and precipitation

A novel hydrometallurgical process was proposed for selective recovery of Cu, Ag, Au and Pd from waste printed circuit boards (PCBs). More than 99% of copper content was dissolved by using two consecutive sulfuric acid leaching steps in the presence of H₂O₂ as oxidizing agents. The solid residue of 2nd leaching step was treated by acidic thiourea in the presence of ferric iron as oxidizing agent and 85.76% Au and 71.36% Ag dissolution was achieved. The precipitation of Au and Ag from acidic thiourea leachate was investigated by using different amounts of sodium borohydride (SBH) as a reducing agent. The leaching of Pd and remained gold from the solid reside of 3rd leaching step was performed in NaClO-HCl-H₂O₂ leaching system and the effect of different parameters was investigated. The leaching of Pd and specially Au increased by increasing the NaClO concentration up to 10 V% and any further increasing the NaClO concentration has a negligible effect. The leaching of Pd and Au increased by increasing the HCl concentration from 2.5 to 5 M. The leaching of Pd and Au were endothermic and raising the temperature had a positive effect on leaching efficiency. The kinetics of Pd leaching was quite fast and after 30 min complete leaching of Pd was achieved, while the leaching of Au need a longer contact time. The best conditions for leaching of Pd and Au in NaClO-HCl-H₂O₂ leaching system were determined to be 5 M HCl, 1 V% H₂O₂, 10 V% NaClO at 336 K for 3 h with a solid/liquid ratio of 1/10. 100% of Pd and Au of what was in the chloride leachate were precipitated by using 2 g/L SBH. Finally, a process flow sheet for the recovery of Cu, Ag, Au and Pd from PCB was proposed.     

Assessment of the leaching of metallic elements in the technology of solidification in aqueous solution

Results are presented of experiments performed to optimize the solidification/stabilization system for metallic elements in aqueous solution. This system involves mixing cement and a solution of metallic elements in a conventional mixer: the paste thus obtained is transferred drop by drop into a recipient filled with an aqueous solution of NaOH at 20% by weight, in which it solidifies immediately. The separate use of chloride solutions of Li+, Cr3+, Pb2+ and Zn2+ makes it possible to obtain granules displaying various levels of compressive strength. Three different inertization matrices were used in the experiments, the first consisting solely of Portland cement, the second of Portland cement and a superplasticizer additive, and the third of Portland cement partially replaced with silica-fume and superplasticizer. The results of the tests performed showed a very low level of leaching into the alkaline solidification solution for Cr3+, the quantity leached being under 2% as against higher levels for the other metallic elements. For all the considered elements, the best results were obtained by using silica-fume in the inertization matrix.     

气化炉渣的重金属浸出特性及化学形态分析

分别采用硫酸硝酸法、水平振荡法和醋酸缓冲溶液法制取气化炉渣的浸出液,考察了不同提取方式对浸出液中重金属质量浓度的影响。采用改进BCR连续提取法对气化炉渣中的重金属Cr,Zn,Cu,Pb,Ni,As,Cd的化学形态进行了分析。实验结果表明：煤气化工艺中的气化炉渣属第Ⅰ类一般工业固体废物;在3种提取方式中,醋酸缓冲溶液法的重金属浸出种类最多,且浸出量最大;Cd和Cr对环境具有较高的潜在危害性,Cu次之,Zn,Pb,Ni,As主要以残渣态形式存在,对环境的直接危害性较低。     

Recovery of metal values from zinc solder dross

Zinc solder dross containing 14.8% Sn, 16.3% Pb, 0.41% Al and 64.5% Zn was leached with 3% H₂SO₄ at 45°C for 1 h. Zinc and aluminum went into solution, whereas lead and tin remained with the residue. Aluminum was selectively precipitated as calcium aluminum carbonate by treating the sulphate leachate with limestone at pH 4.8. Zinc sulphate solution was either evaporated to obtain zinc sulphate crystals or precipitated as basic zinc carbonate at pH 6.8. The undissolved lead and tin were leached with 5 M hot hydrochloric acid. The major part of lead chloride ( 73%) was separated by cooling the leached products down to room temperature. From the soluble fraction, tin was recovered as hydrated tin oxide by alkylation with caustic soda at pH 2.4, while the remaining lead was separated at pH 8.5 as lead hydroxide. A process flowsheet had been suggested which involved two-stage hydrometallurgical treatment. Parameters affecting the recovery efficiency of the suggested method such as temperature, time, pH and acid: solid stoichiometric ratio were investigated. Results obtained revealed that the optimum leaching conditions were achieved by using 20 ml of 3% H₂SO₄ acid/g dross for 1 h at 45°C. Recovery efficiency of the metal salts was 99.1, 99.4, 99.6 and 99.5% for Zn, Al, Pb and Sn respectively. Recovery efficiency was related to the solubility of the concerned salts under the given experimental conditions.