Leaching behaviour of a galvanic sludge in sulphuric acid and ammoniacal media

Leaching behavior and kinetics of beryllium in beryllium-containing sludge (BCS)

Beryllium-containing sludge (BCS) is a byproduct of the physicochemical treatment of beryllium smelting wastewater. The pollutant element beryllium within BCS is highly unstable and extremely toxic, characterized by its small ionic radius and low charge density, resulting in a high risk of leaching and migration. This study is the first to investigate the leaching behavior, influencing mechanisms, and kinetic processes of beryllium in BCS under various environmental conditions. The results indicate that, under national standard conditions, beryllium exhibits a rapid leaching phase within the first 5 h, which then stabilizes after 10 h, with the total leached content significantly exceeding the leaching toxicity identification standards. Under mildly acidic (pH ≤ 5) or highly alkaline (pH = 14) conditions, beryllium demonstrates pronounced leaching and migration behaviors. Notably, in acidic conditions, the leaching rate exceeds 80% within 5 h. Combining the treatment process of beryllium-containing wastewater with analytical methods such as SEM, XPS, ToF-SIMS, and FTIR, it is revealed that due to the heterogeneous nature of BCS, the particle aggregates dissociate over time under acidic conditions. The particle surfaces become increasingly rough, leading to dissolution and the emergence of more reactive sites, resulting in a high proportion of beryllium leaching. Under these conditions, the gradual reaction of Be(OH)2 in BCS to form soluble Be2+ and its hydrolytic complexes is identified as the primary mechanism for extensive beryllium migration. The process encounters minimal diffusion resistance and is classified as reaction-controlled. In acidic conditions with pH = 4, the leaching rate of beryllium significantly increases with rising temperature. The leaching kinetics equation is [(1-x)-0.44]=e(18.26-53050RT)·t, with an apparent activation energy of 53.05 kJ mol-1.

Approaches for the Treatment and Resource Utilization of Electroplating Sludge

The disposal of electroplating sludge (ES) is a major challenge for the sustainable development of the electroplating industry. ESs have a significant environmental impact, occupying valuable land resources and incurring high treatment costs, which increases operational expenses for companies. Additionally, the high concentration of hazardous substances in ES poses a serious threat to both the environment and human health. Despite extensive scholarly research on the harmless treatment and resource utilization of ES, current technology and processes are still unable to fully harness its potential. This results in inefficient resource utilization and potential environmental hazards. This article analyzes the physicochemical properties of ES, discusses its ecological hazards, summarizes research progress in its treatment, and elaborates on methods such as solidification/stabilization, heat treatment, wet metallurgy, pyrometallurgy, biotechnology, and material utilization. It provides a comparative summary of different treatment processes while also discussing the challenges and future development directions for technologies aimed at effectively utilizing ES resources. The objective of this text is to provide useful information on how to address the issue of ES treatment and promote sustainable development in the electroplating industry.

A novel method for effective solidifying chromium and preparing crude stainless steel from multi-metallic electroplating sludge

Electroplating sludge (ES) is a globally prevalent hazardous waste that primarily contains Cr, Cu, Ni, and Fe. However, the residual Cr phases within the slag potentially poses an environmental risk in current vitrification. A novel method for effective recovering and solidifying Cr in ES is proposed in this work. ES was desulfurized and subsequently co-treated with ferrosilicon (Fe-Si) and spent carbon anode (SCA) for enhancing the recovery of Cr, Cu, Ni, and Fe to prepare crude stainless steel. Under optimal conditions, the recovery ratios of Cr, Cu, Ni, and Fe reached 96.96%, 99.45%, 99.92%, and 99.20%, respectively, signifying improvements of 21.4%, 0.2%, 1.5%, and 2.8%, respectively, compared with existing research. Meanwhile, the fluoride in SCA yielded CaF2, further progressing to the Si-Ca-F-Na-Al-O phase, with a solidification ratio of 97.87%. The Cr leaching content of the residual Cr-Cu-S phase in the slag remained below 5 mg/L across a pH range of 2-4, demonstrating enhanced stability compared to prior alloy, oxide, and chemically dissolved phases. An innovative approach for solidify Cr by forming matte holds implications for the treatment of Cr-containing solid wastes such as chromium slag, tannery sludge and stainless steel slag.

Acid-leaching mechanism of electroplating sludge: based on a comprehensive analysis of heavy-metal occurrence and the dynamic evolution of coexisting mineral phases

Electroplating sludge is a typical heavy metal-containing hazardous waste with tens of millions of tons produced annually in China. Acid leaching is the most common method to extract valuable heavy metals for resource recycling and environmental protection. However, the coexisting elements, which are released from electroplating sludge to the leaching solution, will hinder the recycling of valuable heavy metals. In this work, dynamic acid-leaching experiments, X-ray diffraction analysis, and simulation calculations were conducted. It was found that coexisting elements (mainly Ca, Fe, and Al) account for a large proportion, and calcium salts as coexisting mineral phase (especially CaCO3) are ubiquitous in electroplating sludge. Moreover, the evolution of coexisting mineral phase plays an essential role in the acid-leaching process: (1) the dissolution of CaCO3 contributed a strong acid-neutralization capability and released Ca2+; (2) H2SO4 is the optimal extracting reagent, since it triggered the transformation of calcium salts to CaSO4·2H2O, reducing the Ca2+ concentration; (3) the coexisting elements Fe and Al would form ferrous and aluminum salt minerals with the acid-leaching process, which reduces the leaching of low-value elements. This work provides a new perspective on the acid-leaching mechanism of electroplating sludge, where the evolution of the mineral phase effect the release of valuable heavy metals and coexisting elements. This work also provides as comprehensive information as possible on electroplating sludge and inspires the improvement of the acid-leaching method.

Transformation of Zn and Cr during co-combustion of sewage sludge and coals: influence of coal and steam

Combustion experiments of sewage sludge (SS) blended with low-rank coal were conducted through a drop tube furnace (DTF) to explore the effects of low-rank coal type, blending ratio, and steam on the transformation of Zn and Cr. The results showed that the retention rates of Zn and Cr in ash increased from 24.35% and 71.49% for sludge combustion alone to 53.77% and 117.49%, respectively, for coal blended to SS with a mass ratio of 7:3. The greater the proportion of low-rank coal in the fuel, the greater the residual rate of heavy metals in the ash. Meanwhile, rapid diffusion of vapor occupied adsorption sites on metal mineral surfaces, reducing the retention of Zn and Cr in the co-combustion ash. The leaching toxicity analysis of ash showed that the co-combustion ash of SS with coal was free from leaching toxicity hazards in simulated scenarios. The extraction rate of Zn in co-combustion ash increased from 90.72% with hydrothermal acid leaching to 95.46% with microwave-assisted in 2 mol/L H2SO4 extract. The extraction rate of Cr in hydrothermal acid leaching was 62.80%, which was much higher than that in microwave-assisted extraction (31.76%).

Extensive investigation on extraction and leaching kinetics study of Cu and Cr from spent catalyst using acetic acid

The application of organic acids towards the extraction of both Cu and Cr from the Cu-Cr spent catalyst was investigated. A series of organic acid such as acetic acid, citric acid, formic acid, ascorbic acid and tartaric acid were adopted, and after screening, acetic acid showed a profound effect on dissolution of either of the metals over other green reagents. The spent catalyst was characterized by XRD and SEM-EDAX to confirm the existence of the oxide phase due to both Cu and Cr metals. For efficient dissolution of metals, the critical parameters such as agitation speed, acetic acid concentration, temperature, particle size, as well as S/L ratio affecting on it was systematically investigated. It was observed that at approximately 99.99% of Cu along with 62% of Cr was extracted at the optimised conditions (agitation speed: 800 rpm, 1.0 M CH3COOH, 353 K temperature, particle size of (75-105) µm and S/L: 2% (W/V). The leach residue obtained after the first stage of leaching was analysed by SEM-EDAX and XRD, indicating no peaks due to the presence of Cu ensures complete dissolution of Cu at the optimum conditions. Further, to attain the quantitative leaching yield of Cr, the leach residue obtained after the first stage was sequentially investigated using varied acetic acid concentration and temperature. Leaching kinetics was established based on obtained results at the varied operating parameters, and it revealed support for fitting a model of the leaching data to the shrinking core chemical control model (R2 = 0.99) for both metals (Cu and Cr). The activation energy determined to be 34.05 kJ mol-1 and 43.31 kJ mol-1 for Cu and Cr, respectively, validates the proposed leaching kinetics mechanism.

Characterization of ionic liquids removing heavy metals from electroplating sludge: Influencing factors, optimisation strategies and reaction mechanisms

The disposal of electroplating sludge (ES) is a common concern of researchers. Currently, it is difficult to achieve effective fixation of heavy metals (HMs) using traditional ES treatment. As green and effective HMs removal agents, ionic liquids can be used for the disposal of ES. In this study, 1-butyl-3-methyl-imidazole hydrogen sulphate ([Bmim]HSO₄) and 1-propyl sulphonic acid-3-methyl imidazole hydrogen sulphate ([PrSO₃Hmim]HSO₄) were used as washing solvents for the removal of Cr, Ni, and Cu from ES. In reaction with increased agent concentration, solid-liquid ratio, and duration, the amount of HMs eliminated from ES rises, whereas opposite patterns were shown in response to rising pH. The quadratic orthogonal regression optimisation analysis also revealed that the ideal washing specifications for [Bmim]HSO₄ were 60 g L^-1, 1:40, and 60 min, respectively, for agent concentration, solid-liquid ratio, and washing time, while those for [PrSO₃Hmim]HSO₄ were 60 g L^-1, 1:35, and 60 min, respectively. Under the optimal experimental conditions, the Cr, Ni, and Cu removal efficiencies for [Bmim]HSO₄ were 84.3, 78.6, and 89.7%, respectively, and those values for [PrSO₃Hmim]HSO₄ were 99.8, 90.1, and 91.3%, respectively. This was mainly attributed to that ionic liquids enhance metal desorption through acid solubilisation, chelation, and electrostatic attraction. Overall, ionic liquids are reliable washing reagents for ES contaminated by HMs.

A review on fabricating functional materials by electroplating sludge: process characteristics and outlook

As the end product of the electroplating industry, electroplating sludge (ES) has a huge annual output and an abundant heavy metal (HM). The effective disposal of ES is attracting increasing attention. Currently, the widely used ES disposal methods (e.g. landfill and incineration) make it difficult to effectively control of HMs and synchronously utilise metal resources, leading to a waste of metal resources, HMs migration, and potential harm to the environment and human health. Therefore, techniques to limit HMs release into the environment and promote the efficient utilisation of metal resources contained within ES are of great interest. Based on these requirements, material reuse is a great potential means of ES management. This review presents an overview of the process flows, principles and feasibilities of the methods employed for the material reuse of ES. Several approaches have been investigated to date, including (1) additions in building materials, (2) application in pigment production, and (3) production of special functional materials. However, these three methods vary in their treatment scales, property requirements, ability to control HMs, and degree of utilisation of metal resources in ES. Currently, the safety of products and costs are not paid enough attention, and the large-scale disposal of HMs is not concordant with the effective management of HMs. Accordingly, this study proposes a holistic sustainable materialised reuse pattern of ES, which combines the scale and efficiency of sludge disposal and pays attention to the safety of products and the cost of transformation process for commercial application.

Comparative physicochemical analysis of galvanic sludge wastes

The paper provides the physicochemical analysis of galvanic sludge to determine the presence and concentration of toxic metals. Two sludges sampled from the same factory, but from different technological processes, alkaline galvanic sludge obtained from galvanizing process and acidic sludge generated from the chromium plating process were analyzed. Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) revealed increased concentrations of toxic heavy metal ions Zn²⁺, Cr³⁺, Ni²⁺ and Pb²⁺ in the sludge from the galvanizing process and Cr³⁺, Cu²⁺, Ni²⁺, Pb²⁺, Cd²⁺ and Zn²⁺ from the chroming process. Moreover, the sludges were further physicochemically characterized by Reflectance Fourier Transform InfraRed Spectrometry (FTIR), Scanning Electron Microscopy with Energy-dispersive X-ray Spectroscopy Analysis (SEM-EDX) and X-ray diffraction (XRD). The results of ICP-OES were corroborated by FTIR. Analysis of FTIR spectra revealed the specific bands indicating the existence of metal oxides in the analyzed sludges, as well as the presence of organic substances, i.e. solvents and surfactants, used in the electroplating process. The analysis was accomplished following international norms and confirmed the increased concentrations of heavy metal ions from both sludges. In line with the regulations of the Environmental Protection Agency (EPA), the results proved the hypothesis that galvanic sludge is hazardous waste.

Indirect bioleaching recovery of valuable metals from electroplating sludge and optimization of various parameters using response surface methodology (RSM)

Electroplating sludge contains amounts of valuable/toxic metals as a typical hazardous solid waste, but existing technology is hard to simultaneously gain the high recovery of valuable metals and its convert into general solid waste. In this study, indirect bioleaching process was optimized by using RSM for high recovery of four valuable metals (Ni, Cu, Zn and Cr) from electroplating sludge and its shift into general waste. The results showed that the maximum leaching rate respectively was 100% for Ni, 96.5% for Cu, 100% for Zn and 76.1% for Cr at the optimal conditions. In particular, bioleaching saw a much better performance than H₂SO₄ leaching in removal of highly toxic Cr (76.1% vs. 30.2%). The extraction efficiency of Cr by H₂SO₄ leaching sharply rose to 72.6% in the presence of 9.0 g/L Fe³⁺, suggesting that Fe³⁺ played an important role in the bioleaching of Cr. Based on bioleaching dynamics analysis, it was speculated that Fe³⁺ passes through the solid shell and enter inside the sludge to attack Cr assisting by extracellular polymeric substances (EPS), leading to high extraction and low residue of Cr. Meanwhile, due to high-efficient release and removal of valuable/toxic metals by bioleaching, the bioleached residues successfully degraded into general based on TCLP test and can be reused as construction material safely.

Co-treatment of electroplating sludge, copper slag, and spent cathode carbon for recovering and solidifying heavy metals

Electroplating sludge, a hazardous solid waste product of the electroplating industry, presents a serious environmental pollution risk. In this study, an environmentally friendly process for solidifying and recovering heavy metals from electroplating sludge using copper slag and spent cathode carbon is proposed. Combining the results of toxicity characteristic leaching procedure tests, thermodynamic analysis, chemical analysis, X-ray diffraction analysis, and electron probe microanalysis, the Cr, Ni, Cu, Fe, and F transformation mechanisms were first probed during vitrification. Under optimal experimental conditions, the Cr, Ni, and Cu recovery ratios reached 75.56 wt%, 98.41 wt%, and 99.25 wt%, and they increased by 40%, 5%, and 5%, respectively compared with the currently utilized technique. Moreover, the toxicity leaching results of the slag indicate that the Cr, F, and Cu are stable, while Ni is easily leached from the (Fe,Ni)(Fe,Cr)₂O₄ and alloy phases. Under the optimal metal recovery conditions, the leaching concentrations of Cr, Cu, F, and Ni were 0.57 mg/L, 4.45 mg/L, 1.52 mg/L, and 1.85 mg/L, respectively, which can be reused in other materials, minimizing the environmental risk. The electroplating sludge, copper slag, and spent cathode carbon co-treatment process achieves waste disposal with waste and significantly reduces electroplating sludge processing costs.

Selective Complex Precipitation for Ferro-Chrome Separation From Electroplating Sludge Leaching Solution

In this paper, aiming at the problem of chrome-iron separation in electroplating sludge, the separation of ferrochrome by complexation and precipitation with benzoic acid as complexing agent is achieved. The optimal conditions consisted of a 1: 3 molar ratio of Fe³⁺: C₆H₅COOH, a reaction temperature of 30°C, a final pH of 2.5 and a reaction time of 2 min. The separation rate of the iron was 97.38% and the rate of loss of chromium was only 3.59%. The ferrochromium separation products were analyzed by XRD, fluorescence spectroscopy, infrared spectroscopy and H NMR Spectroscopy in order to study the mechanism of precipitation. The results showed that benzoic acid preferentially forms a complex with iron and iron benzoate precipitates with an increase pH. The iron benzoate crystals have a fine particle size, settle rapidly and are easy to filter. The separation of Cr ³⁺/Fe³⁺ was successful using our methodology.

Demetallization of Sewage Sludge Using Low-Cost Ionic Liquids

Sludge produced from wastewater treatment has little to no value and is typically treated through volume reduction techniques, such as dewatering, thickening, or digestion. However, these methods inherently increase heavy metal concentrations, which makes the sludge unsuitable for land spreading and difficult to dispose of, owing to strict legal requirements/regulations concerning these metals. We addressed this problem, for the first time, by using recyclable low-cost protic ionic liquids to complex these toxic metals through a chemical fractionation process. Sewage sludge samples collected from wastewater plants in the UK were heated with methylimidazolium chloride ([Hmim]Cl, triethylammonium hydrogen sulfate ([TEA][HSO₄]) and dimethylbutylammonium hydrogen sulfate ([DMBA][HSO₄]) under various operating temperatures, times and solids loadings to separate the sludge from its metal contaminants. Analysis of the residual solid product and metal-rich ionic liquid liquor using inductively coupled plasma-emission spectrometry showed that [Hmim]Cl extracted >90% of Cd^II, Ni^II, Zn^II, and Pb^II without altering the phosphorus content, while other toxic metals such as Cr^III, Cr^VI and As^III were more readily removed (>80%) with [TEA][HSO₄]. We test the recyclability of [Hmim]Cl, showing insignificant efficiency losses over 6 cycles and discuss the possibilities of using electrochemical deposition to prevent the buildup of metal in the IL. This approach opens up new avenues for sewage sludge valorization, including potential applications in emulsion fuels or fertilizer development, accessed by techno-economic analysis.

Targeted conversion of Ni in electroplating sludge to nickel ferrite nanomaterial with stable lithium storage performance

The recovery of heavy metals from industrial solid waste is of great significance for simultaneously alleviating heavy metal pollution and recycling valuable metal resources. However, the complex compositions of the multiple metallic electroplating waste severely limit the selective recovery of metal resources such as nickel. In this study, a kind of nickel-laden electroplating sludge was taken as an example and the Ni in it was targetedly converted into highly valuable NiFe₂O₄ (nickel ferrite) nanomaterials via a regulator assisted hydrothermal acid-washing strategy, eventually leading to selective extraction of Ni and Ca from the sludge. Sodium carbonate was the best regulator for the formation of NiFe₂O₄, and under the optimal conditions, the extraction rates of Ni and Ca are 96.70 % and 99.66 %, respectively. The as-prepared NiFe₂O₄ nanoparticles exhibited stable electrochemical Li-storage performances, such as a reversible capacity of approximate 316.94 mA h/g at 0.5 A/g and a long cycle life exceeding 100 cycles, with nearly no capacity decay. This work provides a facile and sustainable approach for targeted conversion of heavy metals in industrial solid waste to high-valuable functional materials and selective recovery of heavy metals from multi-metal solid wastes.

Nickel phytomining from industrial wastes: Growing nickel hyperaccumulator plants on galvanic sludges

Nickel (Ni) is used in numerous industrial processes, with large amounts of Ni-rich industrial wastes produced, which are largely sent to landfill. Nickel recovery from waste materials that would otherwise be disposed is of particular interest. Nickel phytomining represents a new technology in which hyperaccumulator plants are cultivated on Ni-rich substrates for commercial metal recovery. The aim of this study was to investigate the possibility of Ni transfer from industrial waste into plant biomass, to support recovery processes from bio-ores. Different industrial galvanic sludges (containing 85-150 g kg^-1 Ni) were converted into artificial substrates (i.e. technosols) and the Ni hyperaccumulator Odontarrhena chalcidica (formerly Alyssum murale) was cultivated on these Ni-rich matrices. A greenhouse pot experiment was conducted for three months including an ultramafic soil control and testing fertilized (NPK) and unfertilized replicates. The results showed that fertilization was effective in improving plant biomass for all the substrates and that O. chalcidica was capable of viably growing on technosols, producing a comparable biomass to O. chalcidica on the control (ultramafic soil). On all technosols, O. chalcidica achieved Ni shoot concentrations of more than >1000 mg Ni kg ^-1 and maximum Ni uptake was obtained from one of the technosols (26.8 g kg ^-1 Ni, unfertilized; 20.2 g kg ^-1 Ni, fertilized). Nickel accumulation from three of the technosols resulted to be comparable with the control ultramafic soil. This study demonstrated the feasibility of transferring Ni from toxic waste into the biomass of Odontarrhena chalcidica and that phytomining from galvanic sludge-derived technosols can provide similar Ni yields as from natural ultramafic soils.

The use of metal hydroxide sludge (in natura and calcined) for the adsorption of brilliant blue dye in aqueous solution

Industrial waste such as metal hydroxide sludge (in natura and calcined) from galvanic bath was evaluated as an adsorbent in the removal of brilliant blue synthetic dye (NB 180) in aqueous solution. The samples were characterised using X-ray fluorescence analysis (XRF), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), as well as the specific surface area (BET) and the point of zero charge (pH_ZCP). The effects of the conditions in relation to pH and adsorbent dosage were also investigated. For the conditions of 5 g.L^-1 and pH of 4, the sludge in natura (LG-IN) reached equilibrium after 60 min, removing 78% of NB 180 dye, while the calcined sample at a temperature of 250°C (LG-250) removed 100% of dye in solution in 30 min. The effect of calcium salts and the leaching study showed that the presence of (Ca²⁺) ions in solution and metal oxides/hydroxides are the main factors responsible for the removal of colour. As for the study of kinetics and adsorption equilibrium, the experimental data were better adjusted to the pseudo-second order models and Freundlich model, respectively. The parameters of the kinetics, equilibrium and intraparticle diffusion models demonstrated a better performance of the sample LG-250 (q_e =4.09 mg.g^-1), when compared to the sample LG-IN (q_e =2.76 mg.g^-1). These results demonstrated that metal hydroxide sludge can be reused and applied in dye removal processes for the treatment of textile effluent.

High-Temperature Permittivity and Microwave Pretreatment Characteristics of Nickel-Containing Sludge from Battery Production

Permittivity is a vitally important parameter for the description of the absorption and heating characteristics of materials under microwave irradiation. In this paper, the permittivity of nickel-containing sludge (NCS), which is created during battery production as a cheap secondary resource, was measured at temperatures from 20 °C to 600 °C at 2.45 GHz using the cavity perturbation method. In addition, the loss tangent (tanδ) and penetration depth (Dp) of microwaves into the material were calculated. The results of the permittivity study show that the dielectric constant (ε′) and dielectric loss factor (ε″) of the NCS increase with increasing temperature. The variations of the loss tangent (tanδ) and penetration depth (Dp) with the temperature can be divided into two parts at 200 °C. The effect of the initial moisture content on the dielectric properties of the material is notably greater than that of the temperature, which was confirmed by the heating curve. After microwave pretreatment, the nickel-containing phase is transformed into NiO, while the weight of NCS is reduced by more than 20%, the particle size is significantly reduced and the leaching time reduce 20 min than that of conventional heating.

Acid extraction of molybdenum, nickel and cobalt from mineral sludge generated by rainfall water at a metal recycling plant

This study investigated the leaching yields of Mo, Ni and Co from a mineral sludge of a metal recycling plant generated by rainfalls. The investigated mineral sludge had a complex heterogeneous composition, consisting of particles of settled soil combined with metal-bearing particles (produced by catalysts, metallic oxides and battery recycling). The leaching potential of different leaching reagents (stand-alone strong acids (HNO3 (68%), H2SO4 (98%) and HCl (36%)) and acid mixtures (aqua regia (nitric + hydrochloric (1:3)), nitric + sulphuric (1:1) and nitric + sulphuric + hydrochloric (2:1:1)) was investigated at changing operational parameters (solid-liquid (S/L) ratio, leaching time and temperature), in order to select the leaching reagent which achieves the highest metal leaching yields. Sulphuric acid (98% H2SO4) was found to be the leachant with the highest metal leaching potential. The optimal leaching conditions were a three-stage successive leaching at 80 °C with a leaching time of 2 h and S/L ratio of 0.25 g L(-1). Under these conditions, the achieved mineral sludge sample leaching yields were 85.5%, 40.5% and 93.8% for Mo, Ni and Co, respectively. The higher metal leaching potential of H2SO4 in comparison with the other strong acids/acid mixtures is attributed to the fact that H2SO4 is a diacidic compound, thus it has more H(+) ions, resulting in its stronger oxidizing power and corrosiveness.

Selective extraction and recovery of rare earth metals from phosphor powders in waste fluorescent lamps using an ionic liquid system

The recycling of rare earth metals from phosphor powders in waste fluorescent lamps by solvent extraction using ionic liquids was studied. Acid leaching of rare earth metals from the waste phosphor powder was examined first. Yttrium (Y) and europium (Eu) dissolved readily in the acid solution; however, the leaching of other rare earth metals required substantial energy input. Ionization of target rare earth metals from the waste phosphor powders into the leach solution was critical for their successful recovery. As a high temperature was required for the complete leaching of all rare earth metals, ionic liquids, for which vapor pressure is negligible, were used as an alternative extracting phase to the conventional organic diluent. An extractant, N, N-dioctyldiglycol amic acid (DODGAA), which was recently developed, showed a high affinity for rare earth metal ions in liquid-liquid extraction although a conventional commercial phosphonic extractant did not. An effective recovery of the rare earth metals, Y, Eu, La and Ce, from the metal impurities, Fe, Al and Zn, was achieved from the acidic leach solution of phosphor powders using an ionic liquid containing DODGAA as novel extractant system.

Effect of Cu species on leaching behavior of simulated copper sludge after thermal treatment: ESCA analysis

The aim of this study is to evaluate the efficiency of thermal treatment on residual copper sludge after separation treatment. The toxicity characteristic leaching procedure (TCLP) concentration, pattern distribution and possible Cu species of simulated copper sludge were analyzed. Parameters such as different reaction time and temperature are also discussed in this study. The TCLP leaching results showed that the TCLP concentration of Cu in thermally treated simulated copper sludge decreased (T=900 degrees C) as the reaction time increased to 4 h. The sequential extraction results showed that the main fraction of raw simulated copper sludge was carbonate. When temperatures were 500 and 700 degrees C, the main fraction of thermally treated simulated copper sludge was also carbonate. The percentage of Fe-Mn oxides and residue increased when T=900 degrees C. Electron Spectroscopy for Chemical Analysis (ESCA) showed that the possible Cu species of raw simulated copper sludge was Cu(OH)(2). The main possible Cu species of thermally treated simulated copper sludge were CuO and Cu(2)O when T was 500 and 700 degrees C, respectively. CuO, Cu(2)O, and Cu(3)O(2) were the possible Cu species in thermally treated simulated copper sludge when T=900 degrees C.

Multiple heavy metals extraction and recovery from hazardous electroplating sludge waste via ultrasonically enhanced two-stage acid leaching

An ultrasonically enhanced two-stage acid leaching process on extracting and recovering multiple heavy metals from actual electroplating sludge was studied in lab tests. It provided an effective technique for separation of valuable metals (Cu, Ni and Zn) from less valuable metals (Fe and Cr) in electroplating sludge. The efficiency of the process had been measured with the leaching efficiencies and recovery rates of the metals. Enhanced by ultrasonic power, the first-stage acid leaching demonstrated leaching rates of 96.72%, 97.77%, 98.00%, 53.03%, and 0.44% for Cu, Ni, Zn, Cr, and Fe respectively, effectively separated half of Cr and almost all of Fe from mixed metals. The subsequent second-stage leaching achieved leaching rates of 75.03%, 81.05%, 81.39%, 1.02%, and 0% for Cu, Ni, Zn, Cr, and Fe that further separated Cu, Ni, and Zn from mixed metals. With the stabilized two-stage ultrasonically enhanced leaching, the resulting over all recovery rates of Cu, Ni, Zn, Cr and Fe from electroplating sludge could be achieved at 97.42%, 98.46%, 98.63%, 98.32% and 100% respectively, with Cr and Fe in solids and the rest of the metals in an aqueous solution discharged from the leaching system. The process performance parameters studied were pH, ultrasonic power, and contact time. The results were also confirmed in an industrial pilot-scale test, and same high metal recoveries were performed.

The bulk composition and leaching properties of electroplating sludge prior/following the solidification/stabilization by calcium oxide

Eighteen samples of electroplating sludge were taken from three vertical profiles of waste storage pond of the zinc plating facility. Dry matter and organic matter content, pH value, bulk concentrations and leachate composition were determined. A sludge sample with the highest zinc value in the leachate was treated with calcium oxide (10% to 70%) and the obtained solidificate was repeatedly tested. There were found significant variations of all measured parameters among the profiles of untreated waste. Dry matter content varied from 125 to 455 mgg(-1), organic matter varied from 94.3 to 293.9 mgg(-1), and pH value varied from 3.42 to 5.90 (mean 4.34). Iron content ranged from 38.4 to 191.4 mgg(-1) (mean 136 mgg(-1); RSD 0.25), while zinc ranged from 10.9 to 58.2 mgg(-1) (mean 33.4 mgg(-1); RSD 0.38). According to its DIN38414-S4 leachate composition, this material was not suitable for landfilling of inert waste since zinc and nickel mean values were 10 and 1.5 times higher, respectively, and maximum values 27 and 2.5 times higher, respectively, compared to the upper permissible limit. Maximum values of Cr(VI), Fe, Ni, Cu, and Zn in the DIN38414-S4 leachate were 0.183 mgL(-1), 34.085 mgL(-1), 1.052 mgL(-1), 0.829 mgL(-1) and 107.475 mgL(-1)L, respectively. Following the solidification/stabilization procedure with CaO (sample/CaO = 90/10), concentrations of Cr(VI), Fe, Cu and Zn were reduced 92, 44, 66 and 57 times, respectively, compared to the untreated sample. The addition of 50% of CaO into the sludge reduced zinc and nickel concentrations 79 and 45 times, respectively, in the DIN38414-S4 leachate of the solidified waste compared to the original sludge, thereby converting an hazardous waste into the inert material suitable for landfilling or reuse in the construction processes.

Preliminary evaluation of galvanic sludge immobilization in clay-based matrix as an environmentally safe process

This study attempts to determine the possibilities and limitations of the immobilization of galvanic wastes by their incorporation into clay-based materials. It focuses on the effects of several processing parameters such as the temperature of thermal treatment, the relative amount of sludge, and the physico-chemical aspects of the sample, on the fixing level of relevant metals (Zn, Ni, Fe, Mn, Pb, Cu, Cr) in thermally treated clay-based samples. The effectiveness of sludge inactivation was assessed by water-leaching test and conductivity measurements. In view of the potential use of the sludge stabilization products as construction materials, the linear shrinkage and bending strain of the fired samples was investigated. To characterize their morphology, mineralogy and composition, fired samples of clay and its mixtures with galvanic sludge were studied on a scanning electron microscope (SEM) coupled with an energy dispersive X-ray analyser (EDS) and X-ray diffractometer (XRD). It was found that the efficiency of metal immobilization is dependent on the clay composition and the temperature of the thermal treatment of the prepared mixtures. The thermal treatment of all samples at all temperatures resulted in the stabilization of all heavy metal ions (copper, nickel, iron, lead, manganese and zinc) with the exception of chromium.

Chemical treatment of sludge: in-depth study on toxic metal removal efficiency, dewatering ability and fertilizing property preservation

The presence of toxic metals in municipal sewage sludge restricts the application of this biomass in agricultural area. A chemical leaching process using a combination of inorganic acid and two oxidants has been developed for sludge decontamination. The present study investigated the effects of the concentrations of sulphuric acid (H2SO4), hydrogen peroxide and ferric chloride on metal solubilization from sewage sludge, as well as preservation of fertilizing properties (nutrient content) and dewatering ability of the treated sludge. The analysis of the results from batch leaching tests has allowed to define the optimal conditions for the reagent concentrations, which are 56 kg Fe3+ tonne(-1) of dry sludge solids (tds), 8 kg H2O2 tds(-1), and enough H2SO4 to reach a pH between 2.0 and 2.5 but less than 142 kg H2SO4 tds(-1). Finally, under these conditions, oxidoreduction potential values are found to be between 450 and 475 mV.