Dissolution Of Heavy Metals Research Articles

Promotion of chloride removal from MSWI fly ash by an accelerated wet-carbonation process to enhance ash recycling in cement manufacture

Chlorides, sulfates, and heavy metals are the three main factors preventing the recycling of municipal solid waste incineration (MSWI) fly ash as an alternative material for cement clinker production, of which chloride plays the main role due to its extremelly hign content in fly ash. This study evaluated three wet-based pretreatment methods (water-washing, CO2-aided washing, and flue gas-aided washing) to remove chlorides using MSWI fly ashes from 13 incineration plants in China. Water washing was suitable for removing Cl- from MSWI fly ash containing a limited amount of less-soluble Cl-containing salts (Ca(OH)Cl, Ca2Al(OH)6(H2O)2Cl, and Ca6(CO3)2(OH)7Cl). However, for fly ash with a significant proportion of these less-soluble Cl-containing salts, injection of CO2/flue gas during washing promoted their decomposition and increased the chloride removal rates by 2–12%. Compared with chloride, the removal rate of sulfate was lower under all treatment scenarios and ranged from 7% to 47%. Therefore, caution should be taken when exploring techniques for the deep removal of chloride from MSWI fly ash, as sulfates may be the limiting factor in fly ash samples with low chloride contents when utilizing the fly ash for cement clinker production. Heavy metals in fly ash were not a limiting factor for any ash samples (either raw ash or treated ash) when utilizing the fly ash for clinker production. However, the dissolution of heavy metals in the washing solution deserves more attention, as a large amount of wastewater will be generated during wet-based pretreatment methods. This study confirmed that CO2/flue gas injection during washing promoted the removal of the less-soluble harmful components of fly ash, expanding the applications of ash materials.

The migration and transformation mechanisms of heavy metals during molten salt cyclic thermal treatment of MSWI fly ash

Molten salt thermal treatment has been demonstrated to be effective in dissolving heavy metals in municipal solid waste incineration (MSWI) fly ash. However, the complex thermochemical reactions of various heavy metals during the process remain unclear. This study investigated the migration and transformation mechanisms of typical heavy metals during molten salt (NaCl-CaCl2) cyclic thermal treatment of fly ash at 600–750 °C, as well as the leaching characteristics and recovery methods of heavy metals in the reacted products. Molten chlorides could be recycled to extract heavy metals from fly ash, which reduced the leaching toxicity of heavy metals in the reacted slags. Over 64.3% of Cd, Cu and Pb in fly ash were transferred to molten salt while the migration rate of Zn was restrained to only 32.3% during the cyclic process at 750 °C. Regarding Cd, Cu, and Pb in molten salt, the chlorination and dissolution of their oxides were significant, while the combination of their chlorides with free O2– to form oxides precipitation was weak. However, the above reaction characteristics of Zn were the opposite. Furthermore, Zn2+ could be stabilized into hardystonite (Ca2ZnSi2O7) in molten salt by reacting with Si2O76- generated from the combination of O2– and SiO2. Besides, increasing the reaction temperature facilitated the chlorination and dissolution of heavy metals. For recovery, heavy metals could be concentrated on the insoluble matters of molten salt, with a maximum concentration of approximately 5 times that in fly ash.

Using restored heavy metal contaminated soil as brick making material: Risk analysis upon different scenarios, considering the completeness of bricks

Restored heavy metal contaminated soil (RHMCS) can be utilized as building material, but the risks of heavy metal dissolution (HMD) under different scenarios are not clear. This study focused on sintered bricks made from RHMCS and assessed the HMD process and utilization risks of whole bricks (WB) and broken bricks (BB) under two simulated utilization scenarios of leaching and freeze-thaw. Part of the studied bricks were crushed, which increased the surface area (SSA) 3.43-fold and exposed the inner heavy metals, increasing the HMD in BB. However, the HMD in sintered bricks did not exceed the “Groundwater Quality Standard” and “Integrated Wastewater Discharge Standard” under different utilization scenarios, although the dissolution processes were different. In the leaching scenario, the release rate of HMs (As, Cr, Pb) changed from fast to slow over time; the maximum concentration was 17% of the standard limits. In the freeze-thaw scenario, there was no significant correlation between the release of HMs and freeze-thaw time, and the HMD of As was the highest, reaching 37% of the standard limits. Further analysis of health risks of bricks in the two scenarios found that the carcinogenic risks (CR) and the non-carcinogenic risks (NCR) were below 9.56 × 10−7 and 3.21 × 10−2, respectively, which are both lower than the Guidelines for Health Risk Assessment of Groundwater Pollution issued by Ministry of Ecology and Environment of China. These findings suggest that the utilization risks of RHMCS sintered bricks analyzed in this study are low in both scenarios, and higher completeness of bricks leads to higher safety in product utilization. The results provide a reference for the engineering utilization and disposal of building materials made from RHMCS.

Redox-Active Polymers as Robust Electron-Shuttle Co-Catalysts for Fast Fe3+/Fe2+ Circulation and Green Fenton Oxidation.

Accelerating the rate-limiting Fe3+/Fe2+ circulation in Fenton reactions through the addition of reducing agents (or co-catalysts) stands out as one of the most promising technologies for rapid water decontamination. However, conventional reducing agents such as hydroxylamine and metal sulfides are greatly restricted by three intractable challenges: (1) self-quenching effects, (2) heavy metal dissolution, and (3) irreversible capacity decline. To this end, we, for the first time, introduced redox-active polymers as electron shuttles to expedite the Fe3+/Fe2+ cycle and promote H2O2 activation. The reduction of Fe3+ mainly took place at active N-H or O-H bonds through a proton-coupled electron transfer process. As electron carriers, H atoms at the solid phase could effectively inhibit radical quenching, avoid metal dissolution, and maintain long-term reducing capacity via facile regeneration. Experimental and density functional theory (DFT) calculation results indicated that the activity of different polymers shows a volcano curve trend as a function of the energy barrier, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap, and vertical ionization potential. Thanks to the appropriate redox ability, polyaniline outperforms other redox-active polymers (e.g., poypyrrole, hydroquinone resin, poly(2,6-diaminopyridine), and hexaazatrinaphthalene framework) with a highest iron reduction capacity up to 5.5 mmol/g, which corresponds to the state transformation from leucoemeraldine to emeraldine. Moreover, the proposed system exhibited high pollutant removal efficiency in a flow-through reactor for 8000 bed volumes without an obvious decline in performance. Overall, this work established a green and sustainable oxidation system, which offers great potential for practical organic wastewater remediation.

Leaching characteristics and solidification strategy of heavy metals in solid waste from natural graphite purification.

The tailings and fluorine-containing sludge were produced during the physical and chemical purification of natural crystalline graphite, containing heavy metals in different occurrence forms. To evaluate the threat of different heavy metals to the environment, this work uses the modified sequential extraction method (BCR) to study the presence of heavy metals in two solid wastes and their dissolution characteristics in different environments. The results show that the pollution risk of heavy metals in graphite tailings to the environment is ranked as Mn > Cr > Ni > Zn, and the pollution risk of Mn in fluorine-containing sludge is higher than that of Cr. This is because the Mn in the two solid wastes mainly exists in the form of weak acid extraction. The leaching number of heavy metals in the two solid wastes is directly proportional to the soaking time and soaking temperature, and inversely proportional to the pH value and the solid-to-liquid ratio. The number of heavy metals dissolved in solid waste landfills is significantly higher than that of acid rain and surface water environments. Based on the above results and the distribution of graphite solid waste, solidification agent was suggested to prevent heavy metal dissolution and reduce environmental risks.

Submicron tourmaline enhanced the solidification of municipal solid waste incineration fly ash by chemical structure reorganization and stabilized heavy metals

Municipal solid waste incineration fly ash (MSWIFA) exsits in large quantitities and contains pollutants such as heavy metal. While solidification is one of the most effective methods for treating MSWIFA, this application is limited by cost, subsequent treatment, and simultaneous immobilization of anions and cations. This research demonstrated that under a certain initial pressure (20 MPa), a gelation reaction involving ball milling-modified tourmaline powder, a small amount of cement clinker, and MSWIFA forms a stable consolidated body and significantly reduces the risk of heavy metal dissolution. The consolidated MSWIFA can easily be formed into unfired bricks in large-scale pilot production, and a response surface model was used to optimize the experimental parameters. When the mass ratio of tourmaline: cement clinker: MSWIFA was 15:15:200 (mixed with a moisture content of 13 to 15 %), the compressive strength of the consolidated body reached 13 MPa, and the amounts of Cr and Pb leached decreased from 12 mg/L to 0.1 mg/L and 25 mg/L to 0.3 mg/L, respectively. The consolidated form contained a new mineral phase (Ca3Si2O7·3H2O, Ca10Mg0.8(SiO4)0.6O2Cl, and CaCl2∙Ca(OH)2·H2O) with a high compressive strength. Notably, the soluble PbSO4 in the MSWIFA was converted into relatively stable PbSiO3, and Cr(VI) was lattice-wrapped. This study was the first to demonstrate that tourmaline synchronously passivates Pb(II) and Cr(VI) in fly ash in the solid phase, with a low cost and requires no subsequent treatment. This study provided a novel technical path for recycling MSWIFA. Eventually, leaching of the heavy metals Pb, Cr, Cu, Cd, and Zn from the solids achieved concentrations less than 0.25, 1.5, 0.5, 0.15, and 100 mg/L.

Preparation of lightweight aggregates using waste soil contaminated with heavy metals: Physical properties, microstructure and verification of heavy metal solidification through different leaching tests

Considerable volumes of polluted soil are being discharged around the world resulting in serious pollution. As both Si and Al are important components in the framework of a lightweight aggregate (LWA), polluted soil can be used as a raw material for preparing the LWA. In this study, LWAs were prepared from polluted soil containing Cu, Cr, Ni, and Pb. Tests were conducted to assess their macroscopic, microscopic, and heavy-metal leaching properties. The mechanism underlying heavy metal dissolution and a method to accelerate this dissolution were systematically studied under the condition of monolithic leaching of the LWAs. The solidification state and leaching process of heavy metals under different conditions of the LWA were investigated. The experimental results indicated that the LWA prepared from polluted soil met the LWA standard and new crystalline phases were formed during the sintering process. At the same time, long-term leaching tests and accelerated leaching tests showed that the leaching concentrations of the four heavy metals were all lower than the safety limits specified in Chinese standards. The experiments revealed that the pH, temperature, and ultrasonication could accelerate the dissolution of heavy metals. In particular, ultrasonication caused the heavy metals to exhibit the effects of long-term leaching in a short time. Nevertheless, leaching amount did not exceed the limits specified by the standard, thus improving the our understanding of heavy metal solidification in LWAs. These results could significantly guide the construction industry in establishing an evaluation method for heavy metal dissolution that conforms to the service environment of LWAs, enabling the safe management of solid wastes and the sustainable development of light aggregates.

Mechanism of simultaneous lead and chromium removal from contaminated wastewater by a schwertmannite-like mineral

In this study, a schwertmannite-like mineral was synthesized for the removal of lead (Pb) and chromium (Cr) from contaminated wastewater. A shaking flask test was performed (150 r/min, 1h) with FeSO4·7H2O, H2O2, Na2SiO3, and CaCl2 added for the mineral synthesis reaction. Results show that optimal performance was achieved with the addition of 1.24g/L FeSO4·7H2O, 0.75g/L H2O2, 1.27g/L Na2SiO3, and 0.44g/L CaCl2 at a water temperature of 28°C, with coexisting ion (Na+, K+, Mg2+) concentrations of 1.50mmol/L and 0.50mmol/L EDTA as a complexing agent. Under these optimal conditions, maximum Pb and Cr removal rates of 95.08% and 97.99%, respectively, were achieved within the first 1min of the mineral synthesis reaction, with the synthesis reaction completed by 6min. The simultaneous removal of Pb and Cr during the schwertmannite-like material synthesis process occurred via electrostatic adsorption and coprecipitation. When the concentration of the complexing agent was increased from 0.75 to 6.03mmol/L, the Pb removal rate decreased from 71.88 to 35.45%, and the Cr removal rate decreased from 95.13 to 75.07%, showing that Pb and Cr removal exhibited significant levels of inhibition. In contrast, varying reaction temperatures induced no significant differences. The Pb and Cr dissolution rates from Pb/Cr-containing schwertmannite-like minerals were 8.18% and 2.86% after 40days, respectively. Therefore, the risk of secondary dissolution of heavy metals is small.

The behavior of heavy metal release from sulfide waste rock under microbial action and different environmental factors.

The dissolution of heavy metals from the waste rock is controlled by many factors. Herein, we investigated the release behavior of iron (Fe), chromium (Cr), copper (Cu), and zinc (Zn) from sulfide waste rock under the actions of microorganisms and different environmental factors (solution pH value, particle size of waste rock, temperature, Fe3+ concentration). The release quantity of heavy metals was negatively correlated with pH and particle size and positively correlated with ambient temperature and Fe3+ concentration. Under the experimental conditions of pH value of 3.0, temperature of 35°C, and waste stone particle size of less than 0.075 mm,, the release quantity of Fe, Cr, Cu, and Zn reached 3680, 18.32, 132.20, 26.60 mg·kg-1 after 20 days of leaching, respectively. Rising the temperature to 45 °C, Fe, Cr, Cu, and Zn release quantities increased to 89.30, 5.81, 105.08, and 28.00 mg·kg-1. Six hundred milligrams per liter Fe3+ increased the release of heavy metals considerably (2.63-65.48 folds). The presence of microorganisms can significantly facilitate the release of heavy metals. Compared to the control group, the release quantities of Fe, Cr, Cu, and Zn increased 4.29, 3.17, 1.54, and 2.39 times, respectively. In addition, the waste rock under microbial action was more seriously corroded than that under chemical factors. The release behavior of these four heavy metals was consistent with the interfacial chemical reaction control model, indicating that the reactions mainly occurred on the surface of the waste rock. This study provides an essential reference for the study of heavy metal leaching behavior.

Effects of abandoned coal mine on the water quality

ABSTRACT Improving effective strategies to control acid mine drainage (AMD) in abandoned mine areas is a significant challenge because of water quality issues. AMD is a serious water pollution problem. The water in the area where the mine is located acquires an acidic character, the pH level of the environment decreases, the concentration of heavy metals increases with their dissolution in the acidic environment, and can cause serious environmental pollution by creating a toxic effect for all living things. However, acidic characteristics are not observed in the waters at high pH levels; a basic environment is formed; the heavy metal dissolution slows down; and the precipitation of minerals begins. In such an environment, it is not possible to observe AMD formation and heavy metal pollution. If AMD source is characterized, the most effective strategies can be developed to control the acidic effluents. The main aim of this work was to investigate the potential impact of Ovacik abandoned, coal mine (Cankiri, Turkey) on the water quality in the areas around the mine. Water samples were collected along the open pit area (abandoned), dump sites and coal storage area. Effluent characterizations were investigated for the better evaluation of the water contamination level to develop the successful treatment strategies. In the studies conducted in the same field in 2010–2011, it was determined that the water pH changes between 6.64 and 8.13. Similarly, in this study, the results showed that the pH values of water streams in the abandoned mine were measured between 7.28 and 8.94 with no heavy metal contamination. Although the coal deposit exhibits AMD source minerals, the rock formations which have alkaline content prevented AMD in the considered site.

The impact of future climate change on water availability in Gusau, Zamfara State, Nigeria

Climate change has continued to pose challenging global environmental problems in the 21st century. For instance, studies have shown that water resources quantity and quality will be seriously degraded by the phenomenon. This paper examines the effect of climate change on future water availability in Gusau City, Zamfara State, Nigeria. The data obtained from three Regional Climate Models (RCMs) ensembles gridded at 0.5o x 0.5o spatial resolutions were used. The analysis was carried out using ArcGIS (ArcMap, version 10.5) software and comparison of the outcome of the three ensembles was made. The findings show future temperature increase as 1- 3oC by 2040, 3oC by 2070 and 2- 5oC by 2100. Furthermore, future rainfall will increase under rcp 4.5 and 8.5 by 6.7% - 20%, 10% - 20% and 10% - 30% by 2040, 2070v and 2100 respectively. It further shows an increase of +10% to + 60% in seasonal changes of rainfall in the months of April-May-June and July-August-September respectively. These will ultimately result in the increase in surface run off and aquifer recharge. Similarly, the quality of water will also be degraded through sedimentation and nitrogen loading from farms, transport and dissolution of heavy metals by flooding. Therefore, the study recommends for the involvement in storm water harvesting and storage processes by both Government and other large scale water users.

Removal of heavy metals in municipal solid waste incineration fly ash using lactic acid fermentation broth.

Municipal solid waste incineration fly ash (MSWIFA) is considered as a hazardous solid waste because of the high mobility of heavy metals. In this study, the removal of heavy metals in MSWIFA using lactic acid fermentation broth (LAFB) under various leaching protocols (i.e. LAFB addition amount and timing) was investigated. Results revealed that compared with that in pure lactic acid solution, the synergistic effect of various substances in LAFB was more favourable to the dissolution of heavy metals. Although the content of acid-soluble heavy metals in MSWIFA decreased after leaching with LAFB, the leaching toxicity measured by acetic acid buffer solution method increased to varying degrees (except that of Cr). Moreover, the maximum leaching concentration of Pb was 14.1 mg/L (standard limit, 0.25 mg/L), which was not conducive to the landfill treatment of MSWIFA. However, if the LAFB-treated MSWIFA was used in cement kiln for co-disposal, the amount of MSWIFA entering the kiln was 6.0 percentage points higher than that in pure water leaching. Therefore, LAFB leaching instead of water leaching is expected to be an effective pre-treatment method for the utilisation of MSWIFA.

Securing Topsoil for Rehabilitation Using Fly Ash in Open-Cast Coal Mines: Effects of Fly Ash on Plant Growth

Rehabilitation is an important stage in mining operations for environmental conservation. However, the shortage of topsoil makesit difficult to achieve rehabilitation in open-cast coal mines. Securing topsoil by mixing soil with fly ash (FA), which is treated asan industrial waste, is expected to solve this issue in coal mines. While mixing soil with FA makes it possible to secure the topsoiland treat industrial waste simultaneously, the high alkalinity of FA and the dissolution of heavy metals from FA may inhibit plantgrowth. This study investigated the effects of FA in the topsoil on plant growth via vegetation tests with simulated topsoil mixedwith FA using Acacia mangium, a species of flowering tree: the FA mixing ratios were set to 0%, 20%, 40%, 60%, and 100%. Thegrowth of Acacia mangium was inhibited with increasing FA mixing ratio, especially from 60% to 80%. However, the growth rate ofAcacia mangium in an FA mixing ratio of 100% was nearly comparable to that in a mixing ratio of 40%. Furthermore, there wereno effects of the physical characteristics and pH conditions in the topsoil on the plant growth at any of the mixing ratios; meanwhile,the accumulated concentration of Al in the plant body increased significantly at an FA mixing ratio of 60%–80%. This suggeststhat the accumulation of Al, which inhibits plant growth, including root growth and its functions, in the plant body inhibited thegrowth of Acacia mangium. Therefore, the most important aspect in terms of rehabilitation concerning the use of FA for securingtopsoil is not the mixing ratio of FA but the amount of Al in the FA and the accumulation of Al in the plant body.

Simultaneous heavy metal removal and sludge deep dewatering with Fe(II) assisted electrooxidation technology

A hybrid sludge conditioning strategy with electrooxidation and Fe(II) addition was used for heavy metal removal from sewage sludge and industrial sludge, with simultaneous sludge dewatering and stabilization. With the addition of 82 mg/g DS Fe(II) and treatment time of 4.5 h, heavy metal removals of 72.95% and 78.49% for Cu, 66.29% and 84.26% for Zn, and 36.52% and 36.99% for Pb were achieved from sewage sludge and industrial sludge samples respectively. The system pH decreased to 2.33 and 2.98 and the oxidation–reduction potential (ORP) values increased to 435.90 mV and 480.60 mV in sewage sludge and industrial sludge samples, respectively, which was conducive to the desorption and dissolution of heavy metals from sludge structures and the degradation of the organic compounds that complexed with heavy metals. In addition, the hybrid conditioning process demonstrated excellent dewatering performance due to the efficient electrochemical disintegration of sludge flocs together with the coagulation of sludge particles by Fe(III) generated via electrooxidation. The strong acidic and oxidative environment produced by the enhanced electrooxidation process was also responsible for pathogen inactivation.

Enhanced Electrokinetic Removal of Heavy Metals from a Contaminated Lake Sediment for Ecological Risk Reduction

ABSTRACT In this study, electrokinetic remediation (EKR) was performed to reduce the risk of heavy metal contaminants viz., Cd, Cu, Ni, Pb and Zn associated with different fractions of lake sediments. Firstly, batch experiments were performed to estimate the optimal concentration of enhancing agents such as EDTA, nitric acid and acetic acid for effective dissolution of heavy metals from sediments and to minimize the dissolution of earth metals (Fe and Al) to maintain good soil health. In addition to that, the effect of pH on dissolution of these heavy metals with optimized concentration was studied separately. The results from batch experiments showed that EDTA with the concentration of 0.01 M enhanced the heavy metal dissolution as 38–88% in the pH range 2–12. Nitric acid and acetic acid with the concentration of 0.05 M enhanced the heavy metal dissolution as 18–85% and 15–80%, respectively in the pH range 2–6. For enhancing agents like nitric acid and acetic acid, the increase of pH (above 6) led to the formation of metal hydroxides and carbonates, which reduced the efficiency of heavy metal dissolution. Secondly, EKR experiments were conducted in a reactor with optimal concentration of EDTA (0.01 M), nitric acid and acetic acid (0.05 M) as electrolyte and sediment saturation solution for 7–21 days of treatment time. After 21 days of EKR with 0.01 M of EDTA as enhancing agent, the average removal of heavy metals achieved about 46.4–78.8 % and associated risk with metals viz., Cd, Pb, Zn and Cu reduced from high to low risk and Ni reduced from high to medium risk, according to risk assessment category. Alternatively, the EKR treatment using nitric acid and acetic acid showed the average removal of heavy metals of about 17.2–43.60% and 24.9–57.2 %, respectively, and all heavy metals pose medium risk, except for Cd, which showed low risk to the environment.

Migration characteristics of heavy metals during simulated use of secondary products made from recycled e-waste plastic

Recycling of plastics from e-waste can conserve resources, however, aging during the use of plastic products can cause the migration of heavy metals in additives. This study presents a methodology for evaluating the risks of heavy metals in waste plastic secondary products during long term use associated with heavy metal migration. The study processes were investigated by: (1) recycling waste plastics and producing secondary products; (2) thermal aging of secondary products; and (3) toxic leaching used to quantitatively analyse the dissolution of heavy metals. Combined with the changes in mechanical properties and microstructure, the effect of aging on the migration of heavy metals was observed. The results showed that the polymer appeared to delaminate, the adhesion of waste plastics to additives decreased, and the mechanical properties clearly decreased after the thermal aging experiment. Leaching experiments showed that the leached concentrations of Ni, Cu, Zn, Pb, and Sb in the three types waste plastic products increased over time. After 8 d of aging, the leached concentrations of Ni, Sb, and Pb exceeded the third, fourth, and third class of the groundwater quality standard, respectively. Specifically, the concentrations of Sb were 141, 289, and 21.1 times higher than the maximum permissible level. Therefore, management hierarchy and safe environmental recycling methods should be developed to reduce the risk of heavy metals in waste plastic secondary products.

Studies on Heavy Metal Dissolution Characteristics from Sediments of Andong Dam

Studies on Heavy Metal Dissolution Characteristics from Sediments of Andong Dam

Interaction of industrial smelting soot particles with pulmonary surfactant: Pulmonary toxicity of heavy metal-rich particles.

Inhalable particles can influence the interfacial behavior of pulmonary surfactant (PS) resulting in various pulmonary diseases. However, the effects of actually airborne particles on the interfacial behavior of PS and its role in the alteration for soluble metal fraction in particles are entirely unexplored. Herein, we investigated the interaction of PS extracted from porcine lungs with smelting soot fine particles as a model of inhaled heavy metal-rich particles. Our results showed that the phase behavior and foamability of PS were obviously altered in the presence of smelting soot fine particles. In addition, the soluble heavy metals in smelting soot fine particles notably increased in the presence of PS as compared to that of saline solution. Further experiments conducted by adding PS's major components (dipalmitoylphosphatidylcholine, DPPC; bovine serum albumin, BSA) demonstrated that comparison of DPPC, adsorbed BSA is beneficial for the dissolution of heavy metals in smelting soot fine particles. Dynamic light scattering experiments verified that the well dispersion of smelting soot fine particles in the presence of BSA may be responsible for the higher solubility of heavy metals. These findings indicate that PS's interfacial behavior change and PS-enhanced solubilization release of metal components may increase the potentially pulmonary risk in the exposure of airborne fine particles enriched with heavy metals.

A Comparative Study of Cement-Bentonite and Cement-Based Remediation of Lead-Contaminated Soils

The mixture of bentonite and cement at a mass ratio of 2:1 (recorded as BC) was used as solidifying agent to repair lead contaminated soil, and traditional cement (PC) was used as contrast solidifying agent. The comparative test results show that the soil restoration and maintenance period reach 7 days and 28 days respectively. Compared with PC solidified soil, the pH and EC value of BC solidified soil is lower, and the pH value and EC value of 4% and 8% BC-solidified soil meet the interval value needed for vegetation growth. The dissolution of heavy metals in BC-solidified soil and PC-solidified soil decreases with the increase of the content of solidifying agent. At the same content, the dissolution of heavy metals in BC-solidified soil is lower, which indicates that the mixed material (bentonite + cement) has better effect on the fixation of heavy metals. The unconfined compressive strength of BC-solidified soil and PC-solidified soil increases with the increase of the content of solidifying agent, but compared with PC-solidified soil, the unconfined compressive strength of BC-solidified soil decreases significantly. Lower unconfined compressive strength is beneficial to the secondary development and utilization of solidified soil. The above research results show that the mixed material of bentonite and cement can effectively fix the heavy metal lead in the soil, avoid the excessive strength of the soil, and consequently cause soil hardening and influence the re-development and utilization. The mixed material is a feasible and economical repair material.

A Study on the Characteristics of Heavy Metal Dissolution by the Aging of Ashes Emissions in the Paper Industry

A Study on the Characteristics of Heavy Metal Dissolution by the Aging of Ashes Emissions in the Paper Industry