High Metal Content Research Articles

Impregnating biochar with Fe and Cu by bioleaching for fabricating catalyst to activate H2O2.

Biochar is an excellent support material for heterogeneous catalyst in Fenton reaction. However, fabrication of heterogeneous catalyst supported by biochar normally adopts chemical impregnation which is costly and difficult in post-treatment. Here, impregnation by bioleaching driven by Acidithiobacillus ferrooxidans was developed. Bioleaching was particularly effective in loading iron to biochar. Iron loading amount was 225.5mg/g after 10-g biochar was treated in bioleaching containing 40-g FeSO4·7H2O for 60h. When copper was added into bioleaching, simultaneous impregnation with iron and copper could be achieved. Impregnation mechanism for iron was jarosite formation on biochar surface and adsorption for copper. For the high metal content, after pyrolysis, the final composites could activate hydrogen peroxide to decolorize dye effectively. With 15mg as-synthesized Cu-Fe@biochar containing 254.3mg/g iron and 33.4mg/g copper, 50mg/L reactive red 3BS or methylene blue could be decolorized completely in 20min in a 100-mL solution by 16-mM H2O2 at pH 2.5. Compared with existing impregnation methods, bioleaching was facile, cheap and green, and deserved more concern. KEY POINTS: • High amount of Fe is loaded to biochar uniformly as jarosite by bioleaching. • Cu is adsorbed onto biochar during bioleaching. • Synthesized Cu-Fe@biochar is an excellent photo-Fenton catalyst.

Analisis Spektrofotometri Serapan Atom pada Penjernihan Air Sumur Bor di Desa Sekernan

Cloudy borehole water if done by filtering method with filtration by sand, charcoal, palm fiber, coral and husks can produce clear water. In the purification process can remove turbidity, color, metal Mn about 98.66 % and Fe around 99,50 %. Zeolite is a mineral that is used as an adsorbent, ion exchanger or catalyst. Zeolite in rice husk ash contains high silica content of 87%-97% and coal ash 50%-69% which is used as an ingredient in the manufacture of zeolite. This study aims to determine the zeolite made from rice husk ash and coal can reduce Fe and Mn levels. Based on the test results of the Health Laboratory Office, samples of water from drilled wells in Sekernan village, RT. 11 with the results of Fe content of 0.475 mg/l and Mn content of 0.380 mg/l. The use of borehole water which has a high metal content for drinking water, bathing and washing can cause a person to suffer from stomach ailments such as diarrhea, skin diseases, such as itching and so on. This research is an experimental study. The results of the water filtration process are left for 30-60 minutes. Furthermore, the water was tested for Fe and Mn levels using Atomic Absorption Spectrophotometry (AAS). The results of the AAS analysis showed that the previous Fe level decreased from 0.475 mg/l to < 0.08 mg/l and the previous Mn level was 0.380 mg/l to < 0.03 mg/l. The purification of borehole water with filtration method can produce clear water. Analysis of the AAS test made from zeolite can reduce the metal content of Mn by about 98.66% and Fe by about 99.50%.

A novel green strategy for biorecovery of valuable elements along with enrichment of rare earth elements from activated spent automotive catalysts using fungal metabolites

Metals recovery from spent automotive catalytic converters (SACCs) has gained great attention due to high metal content of SACCs and their potential to pollute the environment. This study presented a novel green strategy for treating SACCs using oxalic acid-enriched spent culture medium from Aspergillus niger cultivations. To enhance oxalic acid production, the Central Composite Design (CCD) was applied, which demonstrated that glucose (27.06 g/L), NaNO3 (0.9 g/L), disodium oxalate (7.7 g/L), MnSO4·H2O (0.28 g/L), and ethanol (0.65%(v/v)) were the optimum values leading to production of 15.3 g/L oxalic acid. The results of metals biorecovery with the fungal metabolites showed that pulp density of 15 g/L, temperature of 60 °C, and leaching time of 6 h resulted in the highest extraction of 99.1% Al, 99.3% Si, 82.2% Mn, 91.9% Zn, 17.6% Ba, 99.5% Fe, 92.2% Sr, 35.7% Ti, 60.9% Pt, and 73.7% Pd, as well as maximum enrichment of rare earth elements (REEs) in the residual powder. The EDX-mapping analysis indicated that the concentration of ∑REEs was nearly 8% in the initial waste powder, while it reached around 81% in the residual powder after bioleaching. The bioleaching mechanism was further analyzed by characterizing the bioleaching residues through XRD, FTIR, and FESEM analyses.

Recovering metals from flue dust produced in secondary copper smelting through a novel process combining low temperature roasting, water leaching and mechanochemical reduction

Flue dust from secondary copper smelting (FDSC) is a hazardous waste as well as a secondary resource due to the high content of Cl, Br, and valuable metals (Pb, Cu, Zn, Cd). Herein, a novel process, combined low-temperature roasting, water leaching, and mechanochemical reduction, was developed for recovering metals from the FDSC. The phase conversion and behavior of the main elements in the whole process were explored based on thermodynamic analysis, experimental research, and various characterization. First, thermodynamics calculation revealed that adding H2SO4 could significantly decrease the roasting temperature and promote the generation of soluble metal sulfates. The experimental results showed that more than 99% of Cl and Br were removed by roasting at 325 °C and 1.5 times H2SO4 addition. Subsequently, the Cu, Zn, and Cd were almost completely leached by water under the conditions of 80 ℃, 2 h and L/S = 5 mL·g–1, while Pb was rejected and enriched in the residue. Finally, using iron powder as a reductant, 96.7% of PbSO4 was reduced to elemental lead at room temperature with the aid of mechanical force. The findings illustrated that the recovery performance of metals and environmental benefits will be greatly improved by the proposed process.

Origin and Composition of Ferromanganese Deposits of New Caledonia Exclusive Economic Zone

Located in the South-West Pacific, at the northern extremity of the mostly submerged Zealandia continent, the New Caledonian Exclusive Economic Zone (EEZ) covers 1,470,000 km² and includes basins, ridges and seamounts where abundant ferromanganese crusts have been observed. Several investigations have been conducted since the 1970s on the nature and composition of ferromanganese crusts from New Caledonia’s seamounts and ridges, but none have covered the entire EEZ. We present data from 104 ferromanganese crusts collected in New Caledonia’s EEZ during twelve oceanographic cruises between 1974 and 2019. Samples were analysed for mineralogy, geochemical compositions, growth rates, and through a statistical approach using correlation coefficients and factor analysis. Crust thicknesses range from 1 mm to 115 mm, with growth rates between 0.45 mm/Ma and 102 mm/Ma. Based on textures, structures, discrimination plots, and growth rates, we distinguish a group of hydrogenetic crusts containing the highest mean contents of Co (0.42 wt%), Ni (0.31 wt%), and high contents of Mo, V, W, Pb, Zn, Nb, from a group of hydrothermal and/or diagenetic deposits showing high mean contents of Mn (38.17 wt%), Ba (0.56 wt%) and low contents of other trace metals. Several samples from this later group have exceptionally high content of Ni (0.7 wt%). The data shows that crusts from the southern part of the EEZ, notably seamounts of the Loyalty Ridge and the Lord Howe Rise, present high mineral potential for prospectivity owing to high contents of valuable metals, and constitute a great target for further investigation.

Assessing the risk of toxic metals contamination and phytoremediation potential of mangrove in three coastal sites along the Red Sea

Assessing toxic metals (TMs) contamination and phytoremediation potentiality in coastal mangrove lagoons is needed for applying sustainable management of this ecosystem. Consequently, here we determined the pseudo-total content of TMs in the sediments and mangrove plants (leaves, stems, aerial roots, and fine roots) collected from Al-Shuaiba, Yanbu, and Jeddah lagoons, along the coast of Red Sea. The contamination degree was assessed using different indices and the potentiality of mangroves for TMs phytoremediation was determined. The average total metals content (mg kg−1) in the sediments ranged from 1806 to 9580 for Fe, 65 to 195 for Mn, 3.9 to 25.9 for Cu, 5.5 to 16.4 for Zn, 0.09 to 0.42 for Cd, 8.9 to 20.9 for Cr, 32.8 to 37.9 for Ni, and from 0.69 to 6.7 for Pb. The sediments of Yanbu site contained the highest content of all metals (except for Cu), while Al-Shuaiba sediments contained the lowest values. The contamination factor (CF) showed that the sediments of Yanbu and Jeddah suffer from high and moderate contamination degree of Cd. These sites suffer from moderate grade of Ni contamination. The CF values of Fe, Mn, Cr, Cu, and Zn in the three sites were lower than unity, which show low contamination degree. Iron, Cr, Cu, Ni, Pb, and Zn were concentrated in the fine roots, while Cd was concentrated in the stems. Mangrove plants at Yanbu site contained significantly higher content of all metals than the grown plants in Jeddah and Al-Shuaiba sites, which can be explained by the high metal content in the sediments and the anthropogenic metal sources such as the petrochemical industries, and the industrial and municipal wastewater discharged into this site. Sediment-to-plant transfer coefficients values were higher than unity, which indicate that the mangrove plants have the potential to accumulate the metals. The results highlight a potential risk at Yanbu and Jeddah sites and may help for applying sustainable trials for phyto-management of these lagoons.

Geological and Mining Heritage as a Driver of Development: The NE Sector of the Linares-La Carolina District (Southeastern Spain)

Conservation, rehabilitation and post-valuation of the facilities of old mining districts is considered a valid strategy to revitalize these areas. In this study, the northeastern sector of the Linares-La Carolina mining district was analyzed, integrating geological information with mining to assess its value. The characteristics of the three most emblematic veins (consisting of galena, sphalerite, chalcopyrite, pyrite, quartz, ankerite and calcite) were analyzed, namely El Guindo, Federico and El Sinapismo. In this study, each mining exploitation was evaluated according to their geological context. Currently, old mining operations can only be visited from drainage galleries or from some exploration galleries. However, some of the old mining shafts could be adapted for visitation. On the surface, the remains of the most important extraction shafts and part of the associated facilities are still visible. One can also visit old tailings dumps with a high contents of heavy metals associated with ore concentration plants. The contaminating potential of these wastes is being monitored thanks to control piezometers and sensors installed at different depths within the tailings ponds, which assist in controlling evolution in the latter years. Different localities of special interest from geological, mining and mineralogical points of view are indicated. Therefore, the guided tour described in this work is attractive for tourism and educational purposes.

Low-energy electron interaction and focused electron beam-induced deposition of molybdenum hexacarbonyl (Mo(CO)6).

Motivated by the potential role of molybdenum in semiconductor materials, we present a combined theoretical and experimental gas-phase study on dissociative electron attachment (DEA) and dissociative ionization (DI) of Mo(CO)6 in comparison to focused electron beam-induced deposition (FEBID) of this precursor. The DEA and DI experiments are compared to previous work, differences are addressed, and the nature of the underlying resonances leading to the observed DEA processes are discussed in relation to an earlier electron transmission study. Relative contributions of individual ionic species obtained through DEA and DI of Mo(CO)6 and the average CO loss per incident are calculated and compared to the composition of the FEBID deposits produced. These are also compared to gas phase, surface science and deposition studies on W(CO)6 and we hypothesize that reductive ligand loss through electron attachment may promote metal–metal bond formation in the deposition process, leading to further ligand loss and the high metal content observed in FEBID for both these compounds.

A mechanical investigation of perfluorooctane acid adsorption by engineered biochar

Biochar has been engineered to enhance its adsorption for perfluorooctane acid (PFOA). In this study, adsorption of PFOA by engineered biochar derived from feedstocks of switchgrass, water oak leaves and biosolid was investigated. Biosolid biochar had better PFOA adsorption than those of switchgrass and water oak leaves because it had higher contents of O% (26.16–36.59%) and S% (1.03–3.68%) as well as higher metal contents such as Ca, Cu, and Fe. To enhance PFOA adsorption, the biochar was engineered with additives of FeCl3 and carbon nanotube. Carbon nanotube significantly enhanced the surface area of all the engineered biochar by up to 8.5-fold. On the other hand, FeCl3 increased the porosity, pore volume and surface area of plant-based biochar (i.e., switchgrass and water oak leaves). Three adsorption mechanisms, electrostatic interaction, hydrogen bonding, and hydrophobic interaction were responsible for PFOA adsorption. Based on the results of this study, electrostatic interaction was found to play the most important role. Thermodynamic analysis indicated the spontaneous and exothermic reactions occurred during the PFOA adsorption and X-ray spectroscopy results demonstrated that impregnated Fe exhibited as disordered cluster crystals on the surface of engineered biochar. It was concluded that Fe-engineered biochar could significantly improve PFOA adsorption, which had promising potential applications of PFOA removal during wastewater treatment processes.

Environmental Compliance and Nutritional Value of Yakutian Cattle Products

Due to the increasing anthropogenic pollution of the environment, the environmental compliance of agricultural and livestock products becomes increasingly important. This study discusses the materials on pollutant content in the Yakutian cattle products and includes the assessment of the nutritional value of meat and milk. The research objective is to determine the content of toxic metals, microelements, and the nutritional value of meat and milk of Yakutian cattle bred in Yakutia. Research methods. Sample material was analyzed for the content of toxic metals and microelements using atomic absorption spectroscopy. Milk productivity indicators and organoleptic properties of meat were determined by conventional methods. Results. The average value of lead content in meat was determined amounting to 0.1736±0.0076 mg/kg, mercury — 0.0156±0.0012 mg/kg, arsenic — 0.006±0.0007 mg/kg. No cadmium was not found in meat. Relatively high content of toxic metals was detected in liver. The content of microelements (Zn, Cu, Fe) satisfies regulatory requirements. Relatively high content of copper (83.3076±0.2342 mg/kg) and iron (97.4148±0.4412 mg/kg) was detected in liver. Conclusions. Analysis of research results showed that the average values of toxic metals content (mg/kg) (Pb, Cd, Hg, As) in meat and liver satisfy the regulatory requirements. Yakutian cattle meat contains a balanced full range of amino acids and is suitable for the production of high-quality meat products. Yakutian cattle milk has high fat content varying on average from 5.04% to 5.46%.

Comparative analytical study of landfill soil and soil from sanitary protection zone of the solid municipal waste landfill of the Irkutsk city for 2014 and 2019

The largest SMW landfill in the Irkutsk region is that in the Irkutsk city. In 2014, high heavy metal contents were registered in landfill soil samples taken at the landfill site, and it was proposed to perform monitoring outside the landfill in 2019 and determine the pollution distribution area. In this article, the comparative analysis of the degree of heavy metal pollution of the landfill soil and soil from sanitary protection zone is presented. It was established that the studied landfill soil refers to extremely hazardous soils with heavy metal contents that are up to 68 times higher than TLV. Soil samples from the landfill-affected area also contain heavy metals in high concentrations. The manufacturing supervision of the SMW landfill should include the continuous observation of the soil, water, and air condition in the zone of possible impact of the landfill for taking timely environmental protection measures and preventing further negative impact of the landfill on the ecosystem.

Production of aluminum alloy onboard wire with a high content of rare-earth metals produced using electromagnetic crystallization

The Scientific and Production Center for Magnetic Hydrodynamics Ltd has developed an innovative technology for casting long ingots of small diameter (8–12 mm) into an electromagnetic mold (EMM) and manufacturing thin wire (0.5 mm in diameter) from them for onboard wires from 01417 alloy. Crystallization of liquid metal occurs under the influence of electromagnetic forces in an electromagnetic mold with direct supply of coolant to the ingot, due to which cooling rates are achieved that ensure the dispersion of the eutectic phases of rare earth metal aluminides, similarly to how it takes place during the crystallization of granules (~1.103...1.104 K/s). It has been established that the determining parameters in casting ingots are the power supplied to the inductor and the level of the melt above the crystallization front. For the casting to reach a steady state (the process of stabilizing the diameter of the ingot after the start of casting), it is necessary to regulate the melt level for some time. The surface quality of the ingot depends on ensuring stability of the current in the inductor during casting. Fluctuations in the current in the inductor lead to changes in the ingot`s diameter. Casting speed and metal temperature have a great influence on the structure of ingots. In contrast to the method of producing granulated wire with a thin (less than 1 mm) cross-section, which turned out to be problematic due to numerous breaks during drawing associated with the presence of oxide and foreign inclusions, the casting technology in the electromagnetic mold does not require preliminary metal filtration, since oxide and solid non-metallic inclusions are intensively squeezed out by electromagnetic forces onto the ingot`s surface. It has been established that hot deformation of a billet cast in the EMM at the Conform facility provides higher strength characteristics of the wire from the 01417 alloy after drawing compared to the cast annealed billet. Pressing provided an increase in the yield strength and relative elongation of the 01417 alloy by 2 and 2.5 times, respectively, compared with the cast state. As a result, the billet was obtained with high technological plasticity for further drawing. Electron microscopic studies of the wire have been carried out, which have shown that dispersed REM aluminides are rather uniformly distributed over the cross section of the wire with a diameter of 0.5 mm. Determination of the particle size of aluminides at ×50000 magnification showed that their size is ~96–214 nm. Wire from 01417 alloy is used by JSC “Special Design Bureau of the Cable Industry” (JSC “OKB KP”) for the manufacture of conductive cores of installation wires, providing a significant reduction in their weight.

Determination of Nitrate and Fluoride in Spent Pickling Baths for Stainless Steel by Spectrophotometry and Potentiometry

Hydrofluoric and nitric acid baths are widespread in pickling of stainless steel due to their rapid performance and excellent quality of treated surfaces. The concentrations of nitrate and fluoride play an important role in the process and therefore require regular monitoring. Simple methods for spectrophotometric determination for nitrate and potentiometric determination for fluoride were verified based upon current procedures for water analysis. After removing metals by cation exchange, the recoveries were 98.25–98.83% for nitrate and 98.15–100.6% for fluoride. These values were obtained by comparison between these methods and a reference ion chromatography procedure for real baths and the material balance measurements of artificial mixtures. Due to high metal contents in the bath, the proposed methods fail without sample pretreatment; the spectrophotometry of nitrates with sulphosalicylic acid is impossible, and fluoride potentiometry provides the results 20% lower compared to the references samples. The conditions for ion exchange pretreatment (i.e., exchanger capacity, specimen dilution, and flow rate) were optimized. The combination of simple fluoride and nitrate determination with sample pretreatment by cation exchange is suitable for monitoring the bath quality in small pickling plants, where an automatic analyzer would represent a high investment.

Origin of the Shanggong gold deposit, the southern margin of the North China Craton: Constraints from Rb-Sr ages of sericite, and trace elements and sulfur isotope of pyrite

The Shanggong Au deposit is a world-class Au deposit in the southern margin of the North China Craton. Pyrite, as the primary Au carrier in this deposit, is an ideal mineral for dissecting the complex ore-forming process and origin of this deposit. Four types of pyrite were identified by EPMA, SEM, LA-ICP-MS, and NanoSIMS analyses: the coarse-grained cubic, disseminated pyrite (Py1) in the early ore stage (S1) and three types of the fine-grained pentagonal dodecahedron, disseminated pyrite (Py2-1, Py2-2, and Py2-3) with zoning textures in the main ore stage (S2). Py1 is relatively depleted in most metals but enriched in Co and Bi compared with other types of pyrite in S2. On the other hand, both Py2-1 and Py2-3 contain relatively high contents of As, Au, and other metals, whereas Py2-2 contains highest Au, As, Ag, Cu, Sb, Te, Tl, and Pb. Oscillatory zoning in Py2-1 resulted from repeated local fluid phase separation at the near-surface of pyrite crystal due to sharp fluid pressure fluctuation. The Au and As-rich Py2-2 was probably formed under both extrinsic fluctuations in fluid pressure and composition and intrinsic local crystal-fluid interface kinetic effects (e.g., diffusion-limited self-organization, surface electrochemistry-driven adsorption). Crystallization of Py2-1 and Py2-2 has exhausted the metals in the residual fluids, wherein the trace element-poor Py2-3 crystallized and locally replaced Py2-2 through a dissolution-reprecipitation process. Our new data and previous results suggest the ore-forming fluids were likely initial produced by degassing of the concealed pluton, and the metals were sourced from both the crust (e.g., the Taihua complex and Xiong’er Group) and the mantle. The negative δ34S values for pyrite in the S2 stage might result from both the isotopic fractionation between sulfide and sulfate minerals via oxidation of the ore-forming fluid and the input of biogenic sulfur.

Electro-dewatering of steel industrial sludge: Performance and metal speciation

Electro-dewatering (EDW) of sludge has been regarded as an economical and efficient dewatering method in recent years. There have been some studies on municipal sludge and industrial sludge. However, the effects of industrial sludge with high metal and salty content on the EDW performance are still unclear. Here we investigate EDW in the characteristics of steel industrial sludge, which contains large amounts of salts and metals. First, the differences between the steel industrial sludge and the other sludge in EDW treatment were explored. Then, the mechanism of interaction between the transformation of metal speciation and dewatering performance was investigated. The results indicated that the optimal 40.09% moisture content (MC) could be obtained under the operating conditions of 60 V voltage and 2.6 bar pressure. Moreover, the pH variation and electro-redox behavior can lead to the transformation of metal speciation and release charged intermediates relating to metal, causing the rise of current in the EDW process. These phenomena were beneficial to continuous dewatering. By contrast, the speciation of Ca and Zn is mainly affected by electromigration and electroosmotic flow, but the speciation of Fe and Al is more affected by the oxidizing atmosphere. This work extended the application range of EDW and filled the gap of EDW for the industrial sludge field.

Integrated Ecological Assessment of Heavily Polluted Sedimentary Basin within the Broader Industrialized Area of Thriassion Plain (Western Attica, Greece)

The Thriassion Plain, the Saronikos Gulf and Eleusis Bay, Western Attica in Greece, receive pressures from the enormous industrial activity, as well as the Athens metropolitan area and the Piraeus port. Therefore, it is considered as brownfield in the Eastern Mediterranean Sea. The multi-component industrial activity has impacted the soil, the groundwater of Thriassion Plain and the coastal marine sediments of the adjacent Eleusis Bay, part of Saronikos Gulf as well as a brackish lagoon, Koumoundourou Lake. The industrial activity is expressed by high contents of metals, and oil products. This study presents the pollution record of selected published papers that indicate the temporal evolution of legislated polluting compounds, supporting researchers to provide solutions and policy makers to focus on the whole spectrum of potential policy alternatives.

Ultrathick MoS2 Films with Exceptionally High Volumetric Capacitance

AbstractManufacturing electrode films at an industrial‐level submillimeter thickness (≈100 µm) with superior volumetric performance is of practical significance for the commercialization of miniaturized supercapacitor systems. This work proposes a commercially scalable solvated‐ion‐intercalated hydrothermal strategy to demonstrate a record‐high volumetric capacitance (511.29 F cm−3) for supercapacitors based on an industrial‐level submillimeter MoS2 film electrode (94.2 µm). The intercalated solvated Li+ ions increase the amount of negative surface charge and reduce the formation energy of 1T MoS2, leading to a high metallic phase content of 82.7% with enhanced electrical conductivity. Together with the expanded interlayer distance (≈1.23 nm), this allows rapid electron transfer and ion transport in the excessively stacked ultrathick MoS2 film to be simultaneously realized. Thus, the as‐fabricated MoS2||graphene/carbon nanotube asymmetric supercapacitor presents both high energy and power densities, outperforms those of commercial devices, including supercapacitors with submillimeter‐thick electrodes and even micrometer‐thick electrodes.

Forecasting quantities of critical raw materials in obsolete feature and smart phones in Greece: A path to circular economy

Mobile phones represent an ever-increasing waste stream due to the increasing ownership and short lifetime. In particular, smartphones are among the most valuable e-waste because of their extremely high content of numerous key metals, specifically in the printed circuit board and magnets. As feature and smart phones contain different key metals at different concentrations, it is important to distinguish between the two phone types to make reliable estimations. This study presents estimations of obsolete mobile phones quantities, generated in Greece in 1995–2035 and the Critical Raw Materials (CRMs) and Precious Metals (PMs) embedded in them, making a differentiation between feature and smart phones. The dynamic material flow analysis is adopted, the lifespan is evaluated by the Weibull distribution and future sales are predicted by the logistic model incorporating phases of growth, saturation and decline. Then, the future wastes are predicted by the Market Supply A model. According to the results, the generation of obsolete smartphones is constantly increasing, while the waste flows of feature phones are declining. Efficient recycling of obsolete phones (1995–2020) can cover the demand for key metals (Au, Pd, Co) in the new smartphones for more than a decade in Greece, while the demand for Ag, Sb, Si, Zn, Be, Ti will be covered for more than 15 years. In 2020–2035 the accumulated amounts of CRMs and PMs, only from the smartphone waste, will be 1292.02 and 14.11 tonnes, respectively. The findings can contribute to the management of a valuable e-waste category closing the loop between resources-products-wastes.

Carbonation treatment of gasification fly ash from municipal solid waste using sodium carbonate and sodium bicarbonate solutions

In recent years, slagging-gasification technology has received increasing attention in treating municipal solid waste (MSW). Compared with conventional incineration, the higher temperature in the slagging-gasification process optimizes its residue composition, and gasification fly ash (GFA) is the only unreused solid residue. Although GFA is a potential civil engineering material, its high content of heavy metals, chlorides, and sulfates hinders its practical use. Moreover, although carbonation has proven to immobilize heavy metals in incineration fly ash, the conventional gas carbonation method cannot remove chlorides and sulfates. In this study, sodium bicarbonate (NaHCO3) treatment was studied to treat GFA for the first time, and sodium carbonate (Na2CO3) was used for comparison. Different concentrations of NaHCO3 and Na2CO3 solutions were used to treat the GFA, and comprehensive tests were conducted on the treated samples. The results indicated that NaHCO3 treatment was effective in immobilizing Pb, Zn, Cu, and Ni in GFA, while Na2CO3 treatment could not effectively immobilize Pb and Zn. Both NaHCO3 and Na2CO3 promoted the removal of chlorides and sulfates in GFA. The wastewater from the NaHCO3 treatment contained fewer heavy metals compared with those from water washing or Na2CO3 treatment, benefitting its treatment or reuse.

Use of Solar Still in Heavy Metals Removal from Kitchen Wastewater

Indiscriminate discharge of wastewater into the environment can lead to environmental pollution. Heavy metals present in wastewater can infiltrate into the ground to cause groundwater contamination. In this study, a solar still was employed in the removal of heavy metals from domestic wastewater. Five wastewater samples with high heavy metal contents were kept in a solar still and subjected to heat from the sun. The solar still was constructed using locally available materials. The concentration of Iron (Fe), Zinc (Zn), Manganese (Mn), Chromium (Cr) and Cadmium (Cd) in the untreated and treated wastewater samples were determined. The study revealed a drastic reduction in the heavy metal content of the treated wastewater, however, the heavy metal content of most of the treated wastewater samples did not fall within World Health Organization (WHO) limit for potable water. Remarkably, The Zn content of four out of the five treated wastewater samples fell within WHO limit for potable water except for sample 2 which witnessed a drastic reduction from 13.9 to 3.28 mg/L but still did not meet up with WHO limit of 3 mg/L. The treated wastewater can be safely discharged into the environment; however, further treatment is required to make the water safe for human consumption.