Environmental effects of heavy metals derived from the e-waste recycling activities in China: A systematic review

As the world’s leading manufacturing country, China has become the largest dumping ground for e-waste, resulting in serious pollution of heavy metals in China. This study reviews recent studies on environmental effects of heavy metals from the e-waste recycling sites in China, especially Taizhou, Guiyu, and Longtang. The intensive uncontrolled processing of e-waste in China has resulted in the release of large amounts of heavy metals in the local environment, and caused high concentrations of metals to be present in the surrounding air, dust, soils, sediments and plants. Though the pollution of many heavy metals was investigated in the relevant researches, the four kinds of heavy metals (Cu, Pb, Cd and Cr) from e-waste recycling processes attracted more attention. The exceedance of various national and international standards imposed negative effects to the environment, which made the local residents face with the serious heavy metal exposure. In order to protect the environment and human health, there is an urgent need to control and monitor the informal e-waste recycling operations.     

Remediation of acid mine drainage leachate by a physicochemical and biological treatment‐train approach

Biological and physicochemical approaches were utilized in a treatment train for acid mine dis charge (AMD) waters. Anaerobic bioreactors, chemical precipitation reactors, and biopolymer chelation reactors, operated in static, semicontinuous, and continuous flow modes, removed significant quantities of metals and sulfates associated with AMD water. Static tests indicated accept able copper removal via precipitation by generation of hydrogen sulfide in anaerobic reactors. However, low pH affected the biopolymer coating in the chelation reactor, resulting in loss of bed surface. Corrections of AMD to pH > 7 resulted in some metal precipitationprior to biopolymer treatment. A series of static semicontinuous tests at pH 5.0 provided improved metal and sulfate removal. Copper (Cu⁺) was reduced to trace concentrations, while manganese (Mn⁺), although reduced, proved to be the most recalcitrant of the metals. © 2006 Wiley Periodicals, Inc.     

Microbial cycling of iron and sulfur in acidic coal mining lake sediments

Lakes caused by coal mining processes are characterized by low pH, low nutrient status, and high concentrations of Fe(II) and sulfate due to the oxidation of pyrite in the surrounding mine tailings. Fe(III) produced during Fe(II) oxidation precipitates to the anoxic acidic sediment, where the microbial reduction of Fe(III) is the dominant electron-accepting process for the oxidation of organic matter, apparently mediated by acidophilic Acidiphilium species. Those bacteria can reduce a great variety of Fe(III)-(hydr)oxides and reduce Fe(III) and oxygen simultaneously which might be due to the small differences in the redox potentials under low pH conditions. Due to the absence of sulfide, Fe(II) formed in the upper 6 cm of the sediment diffuses to oxic zones in the water layer where itcan be reoxidized by Acidithiobacillus species. Thus, acidic conditions are stabilized by the cycling of iron which inhibits fermentative and sulfate-reducing activities. With increasing sediment depth, the amount of reactive iron decrease, the pH increases above 5, and fermentative and as yet unknown Fe(III)-reducing bacteria are also involved in the reduction of Fe(III). Sulfate is reduced apparently by the activity of spore-forming sulfate reducers including new species of Desulfosporosinus that have their pH optimum similar to in situconditions and are not capable of growth at pH 7. However, generation of alkalinity via sulfate reduction is reduced by the anaerobic reoxidation of sulfide back to sulfate. Thus, the microbial cycling of iron at the oxic-anoxic interface and the anaerobic cycling of sulfur maintains environmental conditions appropriate for acidophilic Fe(III)-reducing and acid-tolerant sulfate-reducing microbial communities.     

Electrokinetic remediation of heavy metal-contaminated soils under reducing environments

This paper describes the migration of hexavalent chromium, Cr(VI), nickel, Ni(II), and cadmium, Cd(II), in clayey soils that contain different reducing agents under an induced electric potential. Bench-scale electrokinetic experiments were conducted using two different clays, kaolin and glacial till, both with and without a reducing agent. The reducing agent used was either humic acid, ferrous iron, or sulfide, in a concentration of 1000 mg/kg. These soils were then spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1000, 500 and 250 mg/kg, respectively, and tested under an induced electric potential of 1 VDC/cm for a duration of over 200 h. The reduction of chromium from Cr(VI) to Cr(III) occurred prior to electrokinetic treatment. The extent of this Cr(VI) reduction was found to be dependent on the type and amount of reducing agents present in the soil. The maximum reduction occurred in the presence of sulfides, while the minimum reduction occurred in the presence of humic acid. The concentration profiles in both soils following electrokinetic treatment showed that Cr(VI) migration was retarded significantly in the presence of sulfides due both to the reduction of Cr(VI) to Cr(III) as well as an increase in soil pH. This low migration of chromium is attributed to: (1) migration of Cr(VI) and the reduced Cr(III) fraction in opposite directions, (2) low Cr(III) migration due to adsorption and precipitation in high pH regions near the cathode in kaolin and throughout the glacial till, and (3) low Cr(VI) migration due to adsorption in low pH regions near the anode in both soils. Ni(II) and Cd(II) migrated towards the cathode in kaolin; however, the migration was significantly retarded in the presence of sulfides due to increased pH through most of the soil. Initial high pH conditions within the glacial till resulted in Ni(II) and Cd(II) precipitation, so the effects of reducing agenets were inconsequential. Overall, this study demonstrated that the reducing agents, particularly sulfides, in soils may affect redox chemistry and soil pH, ultimately affecting the electrokinetic remediation process.     

Effect of maleic acid and pH on the preparation of α-calcium sulfate hemihydrate from phosphogypsum in Mg(NO3)2 solution

Journal of Material Cycles and Waste Management - Phosphogypsum (PG) is a by-product of the wet-process phosphoric acid process, which causes serious environmental issues. In this work, PG was...     

Treatment of acid lignite mine flooding water by means of microbial sulfate reduction

During and after mining activities acidic waters containing high amounts of heavy metals and sulfate often occur. In addition to precipitation processes, water purification is also possible with the help of sulfate-reducing bacteria (SRB). A mixed culture of SRB was adapted to methanol as a cheap carbon source. In order to receive high sulfate-reduction rates immobilization on porous materials proved to be advantageous. Continuous laboratory experiments based on immobilized SRB were carried out with original water from a lignite mining site reaching sulfate-reducing rates up to 132 mg SO4(2-)/(1 h). Based on these results a process for the treatment of such waters was designed. Heavy metals are removed by recycling sulfide containing effluent, excess sulfide can be oxidized to elemental sulfur by addition of hydrogen peroxide. The plant with a 3.9 m3 bioreactor with immobilized SRB was constructed at the mine site. This pilot plant was operated successfully for some months. The removal of heavy metals was close to 100%, the pH of the acidic water increased from 3.0 to 6.9. The sulfate-reducing rate again reached 134 mg SO4(2-)/(1 h). The production of sulfur from the excess sulfide is possible.     

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).     

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.     

Assessment of toxic metals in waste personal computers

Considering the enormous production of waste personal computers nowadays, it is obvious that the study of their composition is necessary in order to regulate their management and prevent any environmental contamination caused by their inappropriate disposal. This study aimed at determining the toxic metals content of motherboards (printed circuit boards), monitor glass and monitor plastic housing of two Cathode Ray Tube (CRT) monitors, three Liquid Crystal Display (LCD) monitors, one LCD touch screen monitor and six motherboards, all of which were discarded. In addition, concentrations of chromium (Cr), cadmium (Cd), lead (Pb) and mercury (Hg) were compared with the respective limits set by the RoHS 2002/95/EC Directive, that was recently renewed by the 2012/19/EU recast, in order to verify manufacturers’ compliance with the regulation. The research included disassembly, pulverization, digestion and chemical analyses of all the aforementioned devices. The toxic metals content of all samples was determined using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The results demonstrated that concentrations of Pb in motherboards and funnel glass of devices with release dates before 2006, that is when the RoHS Directive came into force, exceeded the permissible limit. In general, except from Pb, higher metal concentrations were detected in motherboards in comparison with plastic housing and glass samples. Finally, the results of this work were encouraging, since concentrations of metals referred in the RoHS Directive were found in lower levels than the legislative limits.     

Evaluation of Active Cap Materials for Metal Retention in Sediments

This study evaluated chemically active amendments used to construct active caps for remediating contaminated sediments. Three experiments assessed the effects of apatite, organoclay, zeolite, and biopolymers (chitosan and xanthan) on metal mobility, retention, and speciation. The first showed that the amendments individually and in mixtures (2 percent dry weight) reduced the concentrations of Cr, Co, Ni, and Pb in water extracts from reduced sediment. The second experiment, which used sequential extraction procedures to evaluate the effects of the amendments on metal speciation, showed that the amendments reduced the potentially mobile fractions of Pb, Zn, Ni, Cr, and Cd that are likely to be bioavailable. Last, column studies showed that active caps composed of the amendments prevented the diffusive transport of metals from contaminated sediment over six months. In addition, there was a “zone of influence” beneath the caps in which water extractable concentrations of metals declined substantially compared with untreated sediment. © 2014 Wiley Periodicals, Inc.     

Distribution of remaining Cd in MSWI fly ash washed with nitric acid

Municipal solid waste incineration (MSWI) fly ash is by-product and hazardous waste produced from MSWI plant. In the MSWI fly ash there are high contents heavy metals, among which cadmium (Cd) is more active and toxic. Although inorganic acid leaching is an effective way to remove heavy metals out from the MSWI fly ash and nitric acid has great efficiency for Cd removal, little literature reported the redistribution of remaining Cd in the MSWI fly ash. This investigation focused on the change of different factions (exchangeable, bound to carbonates, bound to Fe–Mn oxides, bound to organic matter and residual) of Cd in treated (i.e. washed with nitric acid) MSWI fly ash. Sequence extraction procedures (SEP) have been used to derive different fractions of Cd, results indicated that fractions of Cd have changed significantly after nitric acid washing procedures. Due to the changes of main compounds and microstructures stable Cd (bound to organic matter and residual) had opportunity to leach out, which resulted in a higher potential risk (or higher bioavailability index) for living creatures, although the total amount of Cd decreased. X-ray diffraction (XRD) and images of scanning electron microscope (SEM) proved these changes in washed MSWI fly ash.     

Metal Concentrations in Pore Water of the Lusatian Lignite Mining Sediments and Internal Metal Distribution in Juncus bulbosus

The aim of this study was to determine a suite of four metals (Fe, Mn, Zn, Cu) in the sediment, porewater and a pioneer plant (Juncus bulbosus) of Lusatian lignite mining lakes in eastern Germany. An attempt was made to understand the factors which affect element concentrations in the above- and below-ground biomass of Juncus bulbosus in an extreme environment. Water samples, sediments, porewater and plant material collected from two different mining lakes dominated by Juncus bulbosus species were analyzed for their elemental content. Additionally, scanning electron microscopy (SEM) and an energy-dispersive X-ray (EDX) detector were used to follow the internal metal distribution in the roots of Juncus plant. Results showed that sediment and porewater element concentrations in the lakes decreased in the order Fe > Mn > Zn and Cu. All the four elements were higher in the roots than in above-ground tissues, suggesting that iron plaque induced on roots under anaerobic conditions served as a metal reservoir, but not as an ultimate mechanism to control metal concentrations in the above-ground tissues. SEM and EDX analyses revealed that the rhizodermis, exodermis and endodermis cells regulate the traffic of transition metals and therefore avoid excess levels that are toxic to the plant in acidic mining-impacted lake sediments.     

Phytoremediation: The uptake of metals and metalloids by rhodes grass grown on metal‐contaminated soil

An experiment was performed to examine the phytoremediation potential of Rhodes grass (Chloris gayana Kunth cv. ‘Pioneer’). The study sought to determine substrate tolerance, biomass production, and plant uptake of antimony (Sb), arsenic (As), cadmium (Cd), lead (Pb), silver (Ag), and zinc (Zn). The plants were grown on weight percent mixtures (5 percent, 15 percent, 25 percent, 35 percent, 50 percent) of a vertisol soil and base‐metal mine tailings (7–2,040 μg/g As, ≥ 30 μg/g Cd, 30–12,000 μg/g Pb, and 72–4,120 μg/g Zn). The 5 percent and 15 percent amendment of mine tailings increased the biomass production of Rhodes grass (from 0.1 g/plant to ≈ 3.5 g/plant) without appreciably elevating plant concentrations of the elements. Plant growth decreased by greater than 50 percent for the substrate containing greater than 25 percent tailings (3,023 μg/g Pb and 1,084 μg/g Zn). Reduced biomass production coincided with maximal Zn uptake by Rhodes grass (249.8 μg/g), indicating tailings induced phytotoxicity. The total concentrations of metals and metalloids tolerated by Rhodes grass in the plant‐growth medium indicated hypertolerance to elevated As, Pb, and Zn concentrations. Partial extraction of the plant‐growth medium determined that plant‐available Pb was ten times higher than Ag, As, Cd, and Zn availability. However, Rhodes grass accumulated low levels of Pb, in addition to As and Cd, over the experimental range, indicating low fodder toxicity risk to browsing livestock. This study concludes that if there are no invasive species issues associated with conservation land uses, Rhodes grass is well suited to metalliferous mined land revegetation and would therefore be highly effective for such programs in subtropical and tropical Australia. © 2005 Wiley Periodicals, Inc.     

Metal releases from a municipal solid waste incineration air pollution control residue mixed with compost

The influence of 10 wt.% mature compost was tested on the heavy metal leachate emissions from a calcium-rich municipal solid waste incineration air pollution control residue (MSWI APC). Apart from elongated columns (500 and 1250 mm), an otherwise norm compliant European percolation test setup was used. More than 99% of the metals Al, As, Cd, Cr, Cu, Fe and Ni were left in the APC residue after leaching to a liquid-to-solid ratio (L/S) of 10. Apparent short-term effects of elevated leachate DOC concentrations on heavy metal releases were not detected. Zn and Pb leachate concentrations were one order of magnitude lower for L/S 5 and 10 from the pure APC residue column, which suggests a possible long-term effect of compost on the release of these elements. Prolonging the contact time between the pore water and the material resulted in elevated leachate concentrations at L/S 0.1 to L/S 1 by a factor of 2. Only Cr and Pb concentrations were at their maxima in the first leachates at L/S 0.1. Equilibrium speciation modelling with the PHREEQC code suggested portlandite (Ca(OH)2) to control Ca solubility and pH.     

Metals in Sediments from the Stockholm Region: Geographical Pollution Patterns and Time Trends

The city of Stockholm is intersected and surrounded by water.Freshwater flows eastward and mixes with slightly brackish water in central Stockholm to finally reach the Baltic Sea. Inorder to estimate the magnitude and geographical impact of Stockholm as a source of metals to the aquatic environments, sediments from 117 stations in the Stockholm region have beenanalysed for metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn).This paper reports on the geographical pollution pattern and onthe time trends in metal pollution in Stockholm during the 20th century. Stockholm is a strong source of Cd, Cu, Hg,Pb and Zn whereas the Cr concentrations are moderately perturbed.In contrast, the concentrations of As, Co, and Ni are in generalclose to preindustrial levels. The concentrations of Cd, Cu, Hg,Pb and Zn are highest in central Stockholm and eastwards (i.e., in the water flow direction). Sediments upstream of Stockholm andin lakes that are not hydrologically connected to central Stockholm show a significantly lower impact. This may be indicative of metals emitted in Stockholm mainly being transported by the water route. Of Cd, Hg, Pb, and Zn, Cd showsthe most pronounced decline in accumulation rates over the lasttwo decades.     

Heavy metal speciation in various types of fly ash from municipal solid waste incinerator

Fly ash (FA) from municipal solid waste incinerators has been known as hazardous waste, which is mostly because of the high content of heavy metal and dioxins. Besides the content, the form of the heavy metals in fly ash is also very important, because it is tightly related with the leaching behavior of fly ash in diverse circumstances. To evaluate the environment potential risk of fly ash, the Tessier chemical extraction method was adopted. In this study, four kinds of fly ash were examined, one sample from China (CFA) and the other three from Japan (RFA, CaFA and NaFA). Five metal elements were detected and they were Ni, Cr, Cd, Pb, and Cu. The result of total heavy metals’ concentration showed CFA has the lowest content. As to the Tessier chemical extraction experiments, the results show that Cd, Pb, and Cu have higher leaching risk in the environment than other heavy metals. The result of leaching test experiment showed that the more exchangeable speciation of Cd, Cr and Pb in FA, the more it could leach out in natural environment.     

Successful full‐scale enhanced anaerobic dechlorination at a NAPL strength 1,1,1‐TCA source area

Bioremediation of 1,1,1‐trichloroethane (TCA) is more challenging than bioremediation of other chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE). TCA transformation often occurs under methanogenic and sulfate‐reducing conditions and is mediated by Dehalobacter. The source area at the project site contains moderately permeable medium sand with a low hydraulic gradient and is approximately 0.5 acre. TCA contamination generally extended to 35 feet, with the highest concentrations at approximately 20 feet. The concentrations then decreased with depth; several wells contained 300 to 600 mg/L of TCA prior to bioremediation. The area of treatment also contained 2 to 30 mg/L of TCE from an upgradient source. Initial site groundwater conditions indicated minimal biotic dechlorination and the presence of up to 20 mg/L of nitrate and 90 mg/L of sulfate. Microcosm testing indicated that TCA dechlorination was inhibited by the site's relatively low pH (5 to 5.5) and high TCA concentration. After the pH was adjusted and TCA concentrations were reduced to less than 35 mg/L (by dilution with site water), dechlorination proceeded rapidly using whey (or slower with sodium lactate) as an electron donor. Throughout the remediation program, increased resistance to TCA inhibition (from 35 to 200 mg/L) was observed as the microbes adapted to the elevated TCA concentrations. The article presents the results of a full‐scale enhanced anaerobic dechlorination recirculation system and the successful efforts to eliminate TCA‐ and pH‐related inhibition. © 2012 Wiley Periodicals, Inc.     

Effects of Decreased Atmospheric Heavy Metal Deposition in South Sweden on Terrestrial Birds and Small Mammals in Natural Populations

In southern Sweden, where exposure to long range distributedheavy metals is about the highest in Scandinavia, depositionsof cadmium (Cd) and lead (Pb) decreased about 20 and 70%,respectively, between mid-1980s and mid-1990s, as estimated bytheir concentrations in moss. Concentrations of Cd and Pb in tissues of the pied flycatcher (Ficedula hypoleuca) and bank vole (Clethrionomys glareolus) were also lower in 1996and 1997 compared to 1981 and 1982. It is concluded that the decreased deposition rate of these elements in southern Sweden had caused decreased exposure, and thus also to decreased potential risk of detrimental effects on insectivorous birds andherbivorous mammals. There was no indication that breeding results of pied flycatcher was influenced by the decreased deposition of toxic metals.     

Metal leachability, heavy metals, polycyclic aromatic hydrocarbons and polychlorinated biphenyls in fly and bottom ashes of a medical waste incineration facility

Medical waste from hospitals and other healthcare institutions has become an imperative environmental and public safety problem. Medical waste in Greece has become one of the most urgent environmental problems, because there are 14,000 tons produced annually, of which only a small proportion is incinerated. In the prefecture of Attica there is only one modern municipal medical waste incinerator (started 2004) burning selected infectious hospital waste (5-6 tons day(-1)). Fly and bottom residues (ashes) are collected and stored temporarily in barrels. High values of metal leachability prohibit the landfilling of these ashes, as imposed by EU directives. In the present study we determined quantitatively the heavy metals and other elements in the fly and bottom ashes of the medical waste incinerator, by inductively coupled plasma emission spectrometry (ICP) and by energy dispersive X-ray analysis (EDAX). Heavy metals, which are very toxic, such as Pb, Cd, Ni, Cr, Cu and Zn were found in high concentrations in both fly and bottom ashes. Metal leachability of fly and bottom ashes by water and kerosene was measured by ICP and the results showed that toxic metals in both ashes, such as Pb, Cr, Cd, Cu and Zn, have high leaching values. These values indicate that metals can become soluble and mobile if ash is deposited in landfills, thus restricting their burial according to EU regulations. Analysis of polychlorinated biphenyls and polycyclic aromatic hydrocarbons in fly and bottom ashes showed that their concentrations were very low. This is the first known study in Greece and the results showed that incineration of medical waste can be very effective in minimizing the most hazardous and infectious health-care waste. The presence of toxic metals with high leachability values remains an important draw back of incineration of medical waste and various methods of treating these residues to diminish leaching are been considered at present to overcome this serious technical problem.     

磷石膏制硫酸钾的新工艺

介绍了由磷石膏制硫酸钾的新工艺：磷石膏与碳酸氯铵在5－30℃下反应,得硫酸铵溶液,该溶液与氯化钾在30℃左右反应,并添加一种有机溶剂,得硫酸钾。低温反应的优点是所得物料便于固液分离,节省加热蒸汽,减少氨挥发。添加某种有机溶剂降低了硫酸钾在体系中的溶解度,使硫酸钾收率提高到90％。此外,采用多釜串联连续反应装置,既提高了设备的生产强度,又使工艺操作条件及产品质量得到稳定。