The ultrasonically assisted metals recovery treatment of printed circuit board waste sludge by leaching separation

This paper provides a practical technique that realized industrial scale copper and iron separation from printed circuit board (PCB) waste sludge by ultrasonically assisted acid leaching in a low cost, low energy consumption and zero discharge of wastes manner. The separation efficiencies of copper and iron from acid leaching with assistance of ultrasound were compared with the one without assistance of ultrasound and the effects of the leaching procedure, pH value, and ultrasonic strength have been investigated in the paper. With the appropriate leaching procedure, a final pH of 3.0, an ultrasonic generator power of 160 W (in 1 l tank), leaching time of 60 min, leaching efficiencies of copper and iron had reached 97.83% and 1.23%, respectively. Therefore the separation of copper and iron in PCB waste sludge was virtually achieved. The lab results had been successfully applied to the industrial scaled applications in a heavy metal recovery plant in city of Huizhou, China for more than two years. It has great potentials to be used in even the broad metal recovery practices.     

非抑制型离子色谱法测定印制电路板表面阳离子污染物

本文提出了一种利用非抑制型离子色谱法测定印制电路板表面五种无机阳离子污染物的方法。样品用异丙醇水溶液提取后,用Sep-PakC18小柱净化试样,用离子色谱分离,电导检测器检测。五种阴离子的检测限介于0.01~0.02μg/ml之间,回收率为98~103%。方法准确、可靠,可用于印制电路板洁净度的评价分析。     

Preparation of Pure Copper Powder from Acidic Copper Chloride Waste Etchant

The method for the recycling of copper from copper chloride solution was developed. This process consists of extraction of copper, purification and particle size reduction. In the first step, reductive metal scraps were added to acidic copper chloride waste enchants produced in the PCB industry to obtain copper powder. Composition analysis showed that this powder contained impurities such as Fe, Ni, and water. So, drying and purification were carried out by using microwave and a centrifugal separator. Thereby the copper powder had a purity of higher than 99% and spherical form in morphology. The copper powder size was decreased by ball milling.     

Factorial experimental design for recovering heavy metals from sludge with ion-exchange resin

Wastewaters containing heavy metals are usually treated by chemical precipitation method in Taiwan. This method can remove heavy metals form wastewaters efficiently, but the resultant heavy metal sludge is classified as hazardous solid waste and becomes another environmental problem. If we can remove heavy metals from sludge, it becomes non-hazardous waste and the treatment cost can be greatly reduced. This study aims at using ion-exchange resin to remove heavy metals such as copper, zinc, cadmium, and chromium from sludge generated by a PCB manufacturing plant. Factorial experimental design methodology was used to study the heavy metal removal efficiency. The total metal concentrations in the sludge, resin, and solution phases were measured respectively after 30 min reaction with varying leaching agents (citric acid and nitric acid); ion-exchange resins (Amberlite IRC-718 and IR-120), and temperatures (50 and 70 degrees C). The experimental results and statistical analysis show that a stronger leaching acid and a higher temperature both favor lower heavy metal residues in the sludge. Two-factors and even three-factor interaction effects on the heavy metal sorption in the resin phase are not negligible. The ion-exchange resin plays an important role in the sludge extraction or metal recovery. Empirical regression models were also obtained and used to predict the heavy metal profiles with satisfactory results.     

Stabilization of Cu in acid-extracted industrial sludge using a microwave process

The leaching concentration of copper ions from the industrial sludge that has been extracted using sulfuric acid may still exceed 15 mg/L, which is the leaching standard of the toxicity characteristic leaching procedure (TCLP) for hazardous waste in Taiwan. Therefore, the acid-extracted industrial sludge is still an important source of hazardous waste. Usually, hazardous waste in Taiwan must be solidified and passed through the TCLP test before it is disposed in a landfill. The aim of this study is to develop a microwave process to stabilize copper ions in the sludge to replace the use of traditional solidification. In this study, two parameters--the reaction time of the microwave process and the additive reagents--were considered. The efficiency of stabilization of the microwave process was evaluated from the result of the TCLP test. The results showed that the stabilization efficiency of copper ions obtained using a microwave process without any added reagent depends highly on the property of the original acid-extracted sludge. Under some conditions, the leaching concentrations were much lower than those of the raw sludge. In additive reagent systems, the results showed that iron powder promoted the stabilization of copper ions more than the other additives such as sodium carbonate and sodium silicate. The leaching concentration of copper ions decreased dramatically from 179.4 to 6.5mg/L below in the iron additive system.     

Theoretic model and computer simulation of separating mixture metal particles from waste printed circuit board by electrostatic separator

Traditionally, the mixture metals from waste printed circuit board (PCB) were sent to the smelt factory to refine pure copper. Some valuable metals (aluminum, zinc and tin) with low content in PCB were lost during smelt. A new method which used roll-type electrostatic separator (RES) to recovery low content metals in waste PCB was presented in this study. The theoretic model which was established from computing electric field and the analysis of forces on the particles was used to write a program by MATLAB language. The program was design to simulate the process of separating mixture metal particles. Electrical, material and mechanical factors were analyzed to optimize the operating parameters of separator. The experiment results of separating copper and aluminum particles by RES had a good agreement with computer simulation results. The model could be used to simulate separating other metal (tin, zinc, etc.) particles during the process of recycling waste PCBs by RES.     

Recovery and reutilisation of copper from metal hydroxide sludges

Sludges generated from electroplating wastewaters contain high concentrations of metals. Studies have confirmed that the concentrations of several metals in the sludge exceed that of those found in natural ores. A very good example is in the case of copper. The natural copper ore contains less than 1% of copper, whereas copper precipitate sludges from the electroplating industry may have an average of 5–10% of copper. Thus, they are one of the largest sources of untapped metal-bearing secondary materials amenable to metals recovery. In Malaysia, most of these metal-bearing sludges are disposed in specially engineering landfills, as many of them do not have the proper incentives and recovery technology. Very less metal recovery is being carried out, and there seems to be a huge waste in these valuable metal resources. With regards to that, an experimental study was carried out to develop and optimise a method of copper recovery from metal hydroxide sludges. Sludge samples containing high concentrations of copper were obtained from a local electroplating plant for the study. A procedure based upon mineral acid leaching or solubilisation was carried out. Two different types of acids, hydrochloric acid (HCl) and sulphuric acid (H₂SO₄) were used to compare the extractability of copper. Experiments were conducted at various acid concentrations and temperatures to determine the maximum amount of copper recoverable. From the results obtained, maximum copper (95%) was solubilised using H₂SO₄ of 10 M at temperature 110°C, for a leaching period of 4 h. These copper concentrated solutions were then heated and crystallised to form CuSO₄ crystals. These crystals were then washed with water and purified. They can be then further treated and reutilised in the metallurgical industry. This study introduces a sustainable method of utilising an electroplating sludge containing valuable metals.     

废线路板的处理技术

对废线路板的危害和废线路板进行处理的必要性以及我国废线路板的来源等进行总结,对线路板的处理方法也进行了概括并对其中具有环保特性的物理处理方法进行了工艺流程的详细较。并对干式物理方法处理废线路板过程中应注意的问题和今后废线路板处理过程的焦点问题给出了作者的看法。     

Immobilization and leaching characteristics of arsenic from cement and/or lime solidified/stabilized spent adsorbent containing arsenic

Solidification/stabilization (S/S) of hazardous iron oxide coated cement (IOCC) spent adsorbent containing arsenic (As(III)) was investigated in the present study. Cement and lime-based S/S effectiveness was evaluated by performing semi-dynamic leach tests. The S/S effectiveness was evaluated by measuring effective diffusion coefficients (D(e)) and leachability indices (LX). It was found that though cement or lime alone were efficient in preventing arsenic leaching (D(e) being in range of 10(-10) to 10(-12) for all the matrices) from the solidified matrices, the best combination for arsenic containment in the matrix was obtained when a mixture of cement and lime was used. The LX values for all the matrices were higher than 10, suggesting that the S/S treated arsenic sludge are acceptable for "controlled utilization". Calcite formation along with precipitation and conversion into non-soluble forms (calcium arsenite, calcium hydrogen arsenate hydrates, calcium hydrogen arsenates, etc.) were found to be the responsible mechanism for low leaching of arsenic from the solidified/stabilized samples. A linear relationship between cumulative fraction (CFR) of arsenic leached and square root of leach time (R(2) ranging from 0.90 to 0.94) suggested that the diffusion is the responsible mechanism for arsenic leaching. Thus, cement and lime show effective containment of the As(III) within the matrix thus indicating S/S by cement and lime, which is also a low-cost option, as a suitable management option for the toxic As(III) sludge.     

Dose-mortality assessment upon reuse and recycling of industrial sludge

This study provides a novel attempt to put forward, in general toxicological terms, quantitative ranking of toxicity of various sources of sludge for possible reusability in further applications. The high leaching concentrations of copper in printed circuit board (PCB) sludge and chromium in leather sludge apparently exceeded current Taiwan's EPA regulatory thresholds and should be classified as hazardous wastes. Dose-mortality analysis indicated that the toxicity ranking of different sources of sludge was PCB sludge>CaF(2) sludge>leather sludge. PCB sludge was also confirmed as a hazardous waste since the toxicity potency of PCB sludge was nearly identical to CdCl(2). However, leather sludge seemed to be much less toxic than as anticipated, perhaps due to a significant decrease of toxic species bioavailable in the aqueous phase to the reporter bacterium Escherichia coli DH5alpha. For possible reusability of sludge, maximum concentrations allowable to be considered "safe" (ca. EC(100)/100) were 9.68, 42.1 and 176 mgL(-1) for CaF(2) sludge, PCB sludge and leather sludge, respectively.     

Inhibition of PCDD/F and PCB formation in co-combustion

Co-combustion of coal-solid waste mixtures in pilot and laboratory-scale combustors with emphasis on monitoring of toxic chlorinated hydrocarbon emissions such as polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) and polychlorinated biphenyls (PCB) is elaborated. The objective of the work is to investigate the so-called primary measures technique. Twenty different thermally resistant inorganic compounds were added directly to the fuel as inhibitors of PCDD/F formation. The fuel-types used in this study included lignite coal, pre-treated municipal solid waste and polyvinyl chloride (PVC). Principle component analysis (PCA) provides the basis for a feasible discussion about the efficiency of 20 inhibitors on PCDD/F and PCB formation. The study showed that the metal oxides group investigated had no inhibitory effect. Although the single N- and S-containing compounds, used as additives for the type of lignite coal, solid waste and PVC fuel, are not very effective as inhibitors, all other N- and S-containing substances are capable to strongly reduce PCDD/F and PCB flue gas emission. The most effective inhibitors are (NH(4))(2)SO(4) and (NH(4))(2)S(2)O(3). (NH(4))(2)SO(4) present at 3% of the fuel can reduce the PCDD/F emissions to 90%. Its low cost and high efficiency favour them as useful for full-scale combustion units.     

Integrated copper-containing wastewater treatment using xanthate process

Although, the xanthate process has been shown to be an effective method for heavy metal removal from contaminated water, a heavy metal contaminated residual sludge is produced by the treatment process and the metal-xanthate sludge must be handled in accordance with the Taiwan EPA's waste disposal requirements. This work employed potassium ethyl xanthate (KEX) to remove copper ions from wastewater. The toxicity characteristic leaching procedure (TCLP) and semi-dynamic leaching test (SDLT) were used to determine the leaching potential and stability characteristics of the residual copper xanthate (Cu-EX) complexes. Results from metal removal experiments showed that KEX was suitable for the treatment of copper-containing wastewater over a wide copper concentration range (50, 100, 500, and 1000 mg/l) to the level that meets the Taiwan EPA's effluent regulations (3mg/l). The TCLP results of the residual Cu-EX complexes could meet the current regulations and thus the Cu-EX complexes could be treated as a non-hazardous material. Besides, the results of SDLT indicated that the complexes exhibited an excellent performance for stabilizing metals under acidic conditions, even slight chemical changes of the complexes occurred during extraction. The xanthate process, mixing KEX with copper-bearing solution to form Cu-EX precipitates, offered a comprehensive strategy for solving both copper-containing wastewater problems and subsequent sludge disposal requirements.     

Production of nickel metal powder from a spent etching solution by solvent extraction and chemical reduction

Nickel metal powder with 99% purity was obtained from a spent FeCl3 etching solution by employing solvent extraction and chemical reduction. Iron and nickel was separated from the spent etching solution by solvent extraction with Alamine336. Iron in the spent etching solution was extracted into the organic phase, while nickel remained in the aqueous solution together with a small amount of iron. After eliminating iron in the aqueous solution by precipitation, nickel metal powder was obtained by chemical reduction with hydrazine at reaction temperature of 100 degrees C and at solution pH of 10.5. Chemical reduction at this specified condition led to nanosized spherical black nickel metal powder with 99% purity.     

PCB钻孔自动光电检测精确配准关键算法

为了实现快速印制电路板（PCB）钻孔自动检测,提出了一种PCB待测板和标准板快速自动配置算法。介绍了PCB钻孔自动光学检测系统的基本结构。采用粗匹配和精匹配两步进行配准的方法,通过边缘提取和Hough变换得到待测板4个角点坐标,利用角点坐标和标准板角点的关系进行粗配准,并找到待测板的定位孔;然后利用待测板定位孔圆心和标准板定位孔圆心的关系进行精确配准。实验证明,该算法计算速度和精度完全能够满足实际要求。     

Recovery of metals from Cuban nickel tailings by leaching with organic acids followed by precipitation and magnetic separation

The percolation leaching of the Cuban nickel tailings containing 0.34% Ni, 0.08% Co and 44.2% Fe was investigated by using tartaric and oxalic acids at different concentrations. About 70% Ni, 80% Co and 30% Fe were extracted after 5 days of leaching with the mixture of 0.15 mol/L tartaric acid and 0.05 mol/L oxalic acid at ambient temperature and normal pressure. Nickel and cobalt extraction of 80% as well as iron extraction of 50% were achieved from the pregnant solution by means of precipitation at 80 degrees C for 2h. The precipitation at ambient temperature led to a similar result after 16 days. Cobalt, nickel and iron oxalates were found in the precipitate by using the X-ray diffraction method. The regeneration of acids during the precipitation step made possible the reuse of the raffinate at the leaching step. Heating of the precipitate at 200 degrees C increased the metal concentration to 1.22% Ni and 0.33% Co, which can be fed in the existing nickel plant in Moa, Cuba. The magnetic processing of the leaching residues led to a non-magnetic product containing less than 20% Fe and a magnetic product containing more than 50% Fe.     

Utilization of water clarifier sludge for copper removal in a liquid fluidized-bed reactor

A method was used to investigate the potential for using water clarifier sludge to remove copper in a fluidized-bed reactor (FBR). This study was conducted to evaluate the removal of copper in an aquatic system without prior treatment. Chemical analyses of water clarifier sludge through inductively coupled plasma-atomic emission spectrophotometry indicated that silicon, aluminum and iron oxides made up more than 84% of this average composition, similar to the composition of clay. The experimental results indicated that the copper removal efficiency was highly dependent on the pH. pH values also influence the character of the water clarifier sludge. After the copper was adsorbed by the water clarifier sludge, the pH of the solution was slightly increased. In the FBR, the copper removal efficiency reached 90% when the initial copper concentration was 20 mg/L, the pH was 4 and the operating time was 60 min. In addition, copper precipitation occured on the surface of clarifier sludge when the initial copper concentration was 20 mg/L and the pH was 7.0. The kinetics of copper ion adsorption at pH 5 showed that 94% copper ion was removed in 60 min and the adsorption equilibrium was attained in 5 h. The mechanisms of adsorption of copper ions on water clarifier sludge including the formation of surface complexation and surface precipitate.     

The removal of arsenic(V) from acidic solutions

The residual concentrations of dissolved arsenic(V) in 1.5% sulphuric acid solutions treated with iron salts and alkaline earth metal compounds have been measured. The results are plotted on triangular composition diagrams covering the composition ranges As 0.2% to 1.2%, Fe 1.0% to 4.0%, alkaline earth metal 3.0% to 6.5%. The results indicate that ferrous iron and lime are the most effective in removing 99.9% of the arsenic over a wide composition range to give residual dissolved arsenic concentrations of ca. 0.5 ppm. Ferric iron is more effective when used in conjunction with mixed calcium and magnesium hydroxides than with lime alone. Ferric iron and dolomite offered the least effective treatment.The effect of lime particle size on the residual dissolved arsenic concentration following ferrous iron-lime treatment was studied. The optimum lime particle size range for arsenic removal was 50–100 μm.Leaching tests were carried out on samples of arsenic bearing sludge from the ferrous iron and lime treatment process mixed with sand chalk and clay soils. The presence of 5,000 ppm of acetic acid in the aqueous leachant did not appear to significantly affect the leaching test results and, after passage through contaminated and uncontaminated soils arsenic concentrations in the leachate were generally below 0.05 ppm. Ferrous iron and lime appeared to be suitable for treating the arsenic solutions and the resulting sludge seemed to be suitable for land disposal.     

Small hazardous waste generators in developing countries: use of stabilization/solidification process as an economic tool for metal wastewater treatment and appropriate sludge disposal

The aim of this study was to propose a profitable destination for an industrial sludge that can cover the wastewater treatment costs of small waste generators. Optimized stabilization/solidification technology was used to treat hazardous waste from an electroplating industry that is currently released untreated to the environment. The stabilized/solidified (S/S) waste product was used as a raw material to build concrete blocks, to be sold as pavement blocks or used in roadbeds and/or parking lots. The quality of the blocks containing a mixture of cement, lime, clay and waste was evaluated by means of leaching and solubility tests according to the current Brazilian waste regulations. Results showed very low metal leachability and solubility of the block constituents, indicating a low environmental impact. Concerning economic benefits from the S/S process and reuse of the resultant product, the cost of untreated heavy metal-containing sludge disposal to landfill is usually on the order of US$ 150-200 per tonne of waste, while 1tonne of concrete roadbed blocks (with 25% of S/S waste constitution) has a value of around US$ 100. The results of this work showed that the cement, clay and lime-based process of stabilization/solidification of hazardous waste sludge is sufficiently effective and economically viable to stimulate the treatment of wastewater from small industrial waste generators.     

Waste Characterization by Scanning Electron Microscopy for Material Recovery

Worldwide legislation coming into force requires considering new waste streams in order to achieve higher targets for material recovery and recycling. It is necessary, therefore, to manage waste materials in which different components are linked together and contaminants of various origins are present. Waste materials thus need to be treated that have a complex and often unknown composition and present different structural, morphological, and chemical properties. The physical and chemical characterization of solid waste is an essential step for the development of suitable treatment strategies, aimed at the recovery of one or more waste components. Scanning electron microscopy appears to be in most cases very helpful for waste characterization, providing information on material size, shape, structure, texture, distribution, and composition. Examples of waste characterization through scanning electron microscopy, finalized to material recovery, are reported. The waste materials taken into consideration include solids of different nature, such as spent lead batteries, cathode ray tubes (CRT), and printed circuit boards (PCB).     

Investigation of the possibility of copper recovery from the flotation tailings by acid leaching

The flotation tailings pond of the Bor Copper Mine poses a great ecological problem not only for the town of Bor but also for the surrounding soils and watercourses. Since the old flotation tailings contain about 0.2% of copper on the average, we investigated their leaching with sulphuric acid in the absence and presence of an oxidant. The aim was to determine the leaching kinetics of copper and iron as affected by various factors such as: the pH value of the leach solution, stirring speed, pulp density, particle size, concentration of ferric ions, temperature and time for leaching. The average copper and iron recovery obtained was from 60% to 70% and from 2% to 3%, respectively. These results indicate that the old flotation tailings pond represents an important source of secondary raw material for the extraction of copper and that it should be valorized rather than land reclamation. At the end of the paper, a mechanism of dissolution of copper and iron minerals from the tailings was described.