Immobilization Of Heavy Metals Research Articles

Migration of spent grain-modified colloidal ferrihydrite: Implications for the in situ stabilization of arsenic, lead, and cadmium in co-contaminated soil

The increase of metal mining, processing, and smelting activities has precipitated a substantial escalation in the contamination of soil by heavy metals. Ferrihydrite (FH) has been commonly used as an amendment for the immobilization of heavy metals in contaminated soil. However, FH suffers from drawbacks such as agglomeration and nonmigratory characteristics, which limit its practical application in soil remediation. Herein, a novel spent grain-modified ferrihydrite (FH-SG) colloidal system was developed, and the FH-SG transport mechanisms in the soil medium were fully studied, focusing in particular on the simultaneous in situ stabilization of arsenic (As), lead (Pb), and cadmium (Cd) in co-contaminated soil. The results showed that the stabilization rates of the FH-SG material reached 94.66%, 96.12%, and 95.52% for water-soluble As, Pb, and Cd, respectively, and 72.22%, 49.39%, and 25.30% for bioavailable As, Pb, and Cd, respectively. The FH-SG material demonstrates notable migration properties in porous media. Theoretical calculation results of a single collector show that the migration deposition of FH-SG material in media is primarily governed by its inherent diffusion characteristics with minimal influence by gravitational forces and media interception. It is noteworthy that the maximum migration distance in quartz sand and soil media with different particle sizes can reach 2.07–2.92 m and 0.78–1.08 m, respectively. Altogether, our findings clearly demonstrate that FH-SG exhibits better stabilization and migration than those of FH alone and most proposed FH colloidal systems. The FH-SG colloidal system holds significant promise for the remediation of various kinds of complex polluted soil.

Enhancement of H2 and light oil production and CO2 emission mitigation during co-pyrolysis of oily sludge and incineration fly ash

The proper treatment and utilization of oily sludge (OS) and incineration fly ash (IFA) remains a significant challenge due to their hazardous nature. To attain effective recovery of petroleum hydrocarbons and synergistic disposal, this study investigated the co-pyrolysis of OS and IFA, resulting in successful energy recovery, CO2 mitigation, and heavy metal immobilization. Results revealed that the peak ratio of light oil to heavy oil fractions reached 179.42% with 20 wt% IFA addition, accompanied by the highest aromatic hydrocarbons selectivity of 30.72% and the lowest coke yield of 106.13 mg/g OS under the optimal temperature of 600 °C. In-depth analysis indicated that IFA inhibited the poly-condensation of macromolecular PAHs and promoted their cracking into light aromatic hydrocarbons. The addition of 50 wt% IFA significantly increased H2 yield (21.02 L/kg OS to 60.95 L/kg OS) and facilitated CO2 sequestration due to its higher content of Ca-bearing minerals. Moreover, high IFA ratios promoted the reduction of Fe species in OS to a low-valence state. Heavy metals in co-pyrolysis char were well immobilized into stable fractions with lower environmental risks. This work highlights the potential of co-pyrolysis as a viable approach for simultaneous disposal of multiple hazardous wastes and offers new insights for their utilization.

Assessing the influence of natural zeolite on toxic heavy metals immobilization and their transfer into Zea mays L.

ABSTRACT. This research presents the efficiency of surfactant-modified (SMNZ) and unmodified natural-zeolite (UNZ) in the immobilization of Cr3+, Pb2+, and Cd2+ in the soil system. Phillipsite is identified as a major component of the host zeolite. Soil mixed with 20% UNZ retained the highest amount of all metals on the top layer of the soil-zeolite column. The lowest transfer of metals into the maize crop was observed at 30 mg of UNZ/kg soil. The experimental conditions such as pH, dose, stirring speed, contact time, and initial metal ions concentration showed significant effect on adsorption of Cr3+, Pb2+, and Cd2+ onto both unmodified and modified zeolite (phillipsite). The maximum adsorption (mg/kg) onto control soil, soil mixed with SMNZ and UNZ was 67.1, 90.9, 151.5 for Cr3+, 84.8, 120.5, 238.1 for Pb2+, 83.3, 116.3 and 212.8 for Cd2+ respectively. Thus, the use of natural zeolite, particularly UNZ has an important role in controlling the mobility of Cr3+, Pb2+, and Cd2+ metal ions in the soil system and thus their transfer to plant system. KEY WORDS: Zeolite, Immobilization, Heavy metals, Column, Pot trial, Batch Bull. Chem. Soc. Ethiop. 2023, 37(6), 1351-1368. DOI: https://dx.doi.org/10.4314/bcse.v37i6.5

Performance optimization design of high ductility cement-based alkali-activated municipal solid waste incineration fly ash composite for rapid repair material

As a residue that results from the high-temperature incineration of urban household waste, municipal Solid Waste Incineration Fly Ash (MSWIFA) contains various harmful organic pollutants like dioxins and heavy metals. These contaminants pose significant health risks to humans, including deformities and carcinogenic effects. The focus of this study is the development of a High Ductility SAC Rapid Repair Material (HD-SACRRM) through MSWIFA as a partial replacement for Sulphate Aluminate Cement (SAC), so as to achieve high ductility, rapid hardening, and the strength required for pavement layers. The reactivity of MSWIFA is investigated by adjusting its content and the type and dosage of alkali-activators. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) tests are conducted to analyze the variety and microstructure of alkali-activated MSWIFA-SAC hydration products. Also, the efficiency of immobilizing heavy metal ions within the alkali-activated system is examined. Based on these findings, the proportions of HD-SACRRM are optimized. The experimental results demonstrate that the optimal conditions for MSWIFA reactivity are met when the MSWIFA content is 20% and the 30% soluble silicate with a modulus of 1.8 is present. The optimized conditions of HD-SACRRM are as follows: a 20% MSWIFA content, 30% soluble silicate with a modulus of 1.8, a water-cement ratio of 0.30, a 2.0% fiber volume fraction, a sand-cement ratio of 0.30, and 5% Li2CO3 as an early strength agent. After 48 h of curing as standard, the material exhibits a compressive strength of 45.7 MPa, an ultimate elongation of 2.70%, and an average crack width of 127.59 μm. The alkali-activated MSWIFA-SAC system generated more gels such as C-S-H and C-A-H, thus resulting in a dense microstructure that enhances both the capacity of heavy metal immobilization and mechanical strength. These findings shed some light on the recycling of MSWIFA solid waste and the repair of asphalt concrete road surfaces.

Bioremediation of PBDEs and heavy metals co-contaminated soil in e-waste dismantling sites by Pseudomonas plecoglossicida assisted with biochar

Biochar-assisted microbial remediation has been proposed as a promising strategy to eliminate environmental pollutants. However, studies on this strategy used in the remediation of persistent organic pollutants and heavy metals co-contaminated soil are lacking, and the effect of the combined incorporation of biochar and inoculant on the assembly, functions, and microbial interactions of soil microbiomes are unclear. Here, we studied 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47) degradation and heavy metal immobilization by and biochar-based bacterial inoculant (BC/PP) in an e-waste contaminated soil, and corresponding microbial regulation mechanisms. Results showed that BC/PP addition was more effective in reducing Cu and Pb availability and degrading BDE-47 than inoculant alone. Notably, BC/PP facilitated bound-residue formation of BDE-47, reducing the ecological risk of residual BDE-47. Meanwhile, microbial carbon metabolism and enzyme activities (related to C-, N-, and P- cycles) were enhanced in soil amended with BC/PP. Importantly, biochar played a crucial role in inoculant colonization, community assembly processes, and microbiome multifunction. In the presence of biochar, positive interactions in co-occurrence networks of the bacterial community were more frequent, and higher network stability and more keystone taxa were observed (including potential degraders). These findings provide a promising strategy for decontaminating complex-polluted environments and recovering soil ecological functions.

Production of glass-ceramics from MSW-fly ash and Dexing copper mine-tailing: Crystallization kinetics, structure, properties and immobilization of heavy metals

To reduce the environmental pollution from MSW-fly ash and Dexing copper mine-tailing and realize their maximum utilization, this research used them to synthesize novel eco-friendly glass-ceramics. Effects of different nucleation-crystallization temperatures on the crystal evolution, microstructure, properties, leaching behavior of heavy metals were discussed. The findings indicate that the crystallization activation energy E is 381 kJ/mol, and the crystallization mechanism is two-dimensional crystallization controlled by diffusion with an increasing nucleation rate. The difference in the nucleation-crystallization temperature will affect the precipitation and growth of crystal (CaAl2Si2O8) in this glassy system, and further affect the microstructure and properties of the prepared glass-ceramics. Furthermore, because the glass-ceramics is the combination of glass and crystal, an obvious immobilization effect for heavy metals Fe, Mn and Cr can be obtained in our glass-ceramics. Apart from the high immobilization efficiencies for heavy metals, our glass-ceramics also show low density (2.715–2.761 g/cm3) and water absorption (0.026–0.045%), high Vickers hardness (5.72–6.39 GPa), good chemical stability (kH2SO4: 3.68–28.72%, kNaOH: 0.01–0.96%), which confirms the potential and feasibility of the MSW-fly ash-Dexing copper mine-tailing-derived glass-ceramics as building decoration material.

Modification of phases evolution and heavy metal immobilization in alkali-activated MSWI FA by the incorporation of converter steel slag

Municipal solid waste incineration fly ash (MSWI FA) poses serious environmental concerns due to its high content of hazardous organics, heavy metals, and soluble salts. This study aimed to solidify the harmful components in MSWI FA by alkali activation and explore the influence of converter steel slag on the phase evolution. With the increase of curing time, the amount of C-(A)-S-H gel increased and its microstructure shifted to a high crystalline and crosslinked state, accompanied by the increase of Ca/Si ratio. The addition of steel slag was beneficial to the formation of C-(A)-S-H gel and enhanced its crystallinity and crosslinking degree. Compared with alkali-activated MSWI FA, NaCl and KCl content decreased more significantly with curing time and Friedel ’salts were found in the matrix modified by steel slag. The leaching toxicity of heavy metals in alkali-activated matrix was reduced as curing time increased. The increase of C-(A)-S-H gel content and changes of its microstructure were conducive to the stabilization of heavy metals and chlorides. The refinement of pore size and improvement of compressive strength contributed to the physical encapsulation of heavy metals and chlorides.

Red mud/silica sand tailing-derived glasses and glass-ceramics for architectural decoration: crystallization, structure, properties and immobilization of heavy metals

To achieve high-efficiency utilization of red mud (RM) and silica sand tailing (SST), this work used them to prepare glasses and glass-ceramics with different mass ratios of RM/SST. The crystallization kinetics, crystal evolution, structure, properties, and the immobilization of heavy metals were studied. The results show that the parent glasses’ activation energies for crystallization are in the range of 371.77–414.03 kJ/mol, and the crystallization mechanisms should be the bulk crystallization or the combination of surface and bulk crystallization. With the increase of SST content, the main crystal phase in the glass-ceramics will change from NaAlSiO4 to (Ca,Na)(Si,Al)4O8, which further results in the variations of structure and properties. By comparison, it is found that the glass–ceramic GCRS6/4 shows the best properties, including low density and water absorption, high bending strength, excellent acid and alkali-resistance. In addition, the GCRS6/4 also shows high immobilization efficiencies for heavy metals including Fe3+, Cu2+, Zn2+, Pb2+ and Cr3+ ions. This investigation not only achieved the high-efficiency utilization of RM and SST, but also produced a novel eco-friendly glass–ceramic material for architectural decoration.

Effect of willow biochar and fly ash-derived zeolite in immobilizing heavy metals and promoting enzymatic activity in a contaminated sandy soil

Great difficulties associated with the reclamation of contaminated soils make it necessary to improve its methods and search for new, innovative technological solutions. Both biochars and synthetic zeolites have properties to control the mobility, and bioavailability of heavy metals in the soil through surface adsorption, ion exchange, or complexation. The aim of this study was to determine the effectiveness of soil supplementation with biochar and zeolite in immobilizing heavy metals (Cd, Pb, Zn) and promoting enzymatic activity in contaminated loamy sandy soil. The study was conducted on biochar produced from plant (willow) biomass at 350 °C and 550 °C, zeolite hydrothermally synthesized from fly ash and obtained from conventional coal combustion, as well as mixtures of these materials. Experimental pots were filled with loamy-sandy soil. The soil was contaminated with the following toxic metals: Cd, Pb, and Zn. Two factors were used in the experiment: (i) grass species (Dactylis glomerata L., Festuca arundinacea Schreb.) and (ii) soil treatment. Soil supplementation with functionalized materials reduced the share of mobile and carbonate-bound forms of cadmium, lead, and zinc. The study indicated that functionalized materials, such as biochar and zeolite, are moderately effective when used separately, but better results can be obtained by applying these materials together as mixtures. The results of the two-year study carried out on soil freshly contaminated (spiked) with heavy metals proved that the time after which significant changes in the bioavailable metal contents are observed is an important element in the assessment of soil supplementation with functionalized materials. The beneficial effect of the applied functionalized materials and their mixtures in promoting soil enzymatic activity is closely related to the effect of these materials on the chemical properties, such as pH or EC. Therefore, in addition to the chemical properties of contaminated soils, the design of heavy metal immobilization processes should also consider the microbial response as a key element in restoring soil health.

Evaluation of the mobility of heavy metals in the sediments originating from the post-galvanic wastewater treatment processes.

The article presents the assessment of heavy metals mobility in sediments from the process of galvanic wastewater treatment (pH 2.5, Co 1.5mg/L, Cr6+ < 0.02mg/L, Cr(total) 62mg/L, Cu 110mg/L, Ni 129mg/L and Pb 59mg/L) based on the use of hydroxides (Ca(OH)2, NaOH) as well as inorganic and organic sulphur compounds (Na2S, sodium dimethyldithiocarbamate (DMDTC), sodium trithiocarbonate (Na2CS3), trimercapto-s-triazine trisodium salt, TMT). The leachability was assessed after 1, 7, 14 and 21days of sediment contact with the leaching agent (deionized water). FeCl3 was used as a coagulant. The efficiency of metal removal changed within a range of 99.67-99.94% (for NaOH), 98.80-99.75% (for TMT), 99.67-99.92% (for DMDTC), 99.67-99.91 (for Na2CS3). The heavy metal content in the obtained precipitates changed within the following ranges: 0.1-0.2g/kg (Co), 9.8-14.7g/kg (Cr), 23.6-39.8g/kg (Cu) 30.5-43.2g/kg (Ni), 24.3-33.1g/kg (Pb) and 12.2-18.7g/kg (Cd). The leachability tests revealed the release of 34-37% of Cd, 6.4-7.5% of Ni and 0.06-0.07% of Cu after using an excess of Na2CS3 as the precipitant. The use of NaOH resulted in the release of 0.42-0.46% of Cr from the sediment, and the use of TMT 0.03-0.34% of Ni. The best immobilization of heavy metals was observed in the case of the precipitate resulting from the use of DMDTC as a precipitating agent. The findings may be useful for predicting the mobility of heavy metals in the sludge and assessing the risk involved so as to support their removal and management.

Remediation of Heavy Metal (Cu, Pb) Contaminated Fine Soil Using Stabilization with Limestone and Livestock Bone Powder

Soil environments contaminated with heavy metals by typhoon flooding require immediate remediation. High-pressure soil washing using water could be a viable short-term solution for cleaning soil contaminated with heavy metals. Soil washing employing high-pressure generates heavy metal contaminated fine soil and wastewater. This contaminated fine soil cannot be reused without proper treatment because of the high levels of heavy metal contamination. Stabilization was used for immobilizing heavy metals (Cu, Pb) in the contaminated fine soil. The stabilizing agents used for immobilizing heavy metals (Cu, Pb) in the contaminated fine soil included two types of limestone (Ca-LS and Mg-LS) and livestock bone powder (LSBP). The Ca-LS, Mg-LS, and LSBP were applied to the contaminated fine soil at dosages in the range of 2 wt%~10 wt%. Two different particle sizes (-#10 vs. -#20 mesh) and curing times (1 week vs. 4 weeks) were used to compare the effectiveness of the stabilization. Extractions using 0.1 N HCl were conducted to evaluate the stabilization effectiveness. Heavy metal leachability was significantly decreased with higher Ca-LS and LSBP dosages. The LSBP treatment was more effective than the Ca-LS and Mg-LS treatments and the Mg-LS showed the poorest performance. The highest degree of immobilization was attained using a 10 wt% LSBP (-#20 mesh), resulting in an approximate leachability reduction of 99% for Pb and 92% for Cu. The -#20 mesh material and 4 weeks of curing were more effective than the -#10 mesh material and 1 week of curing, respectively. The SEM-EDX results showed that metal precipitates and pyromorphite like phases could be responsible for effective heavy metal immobilization. This study suggests that Ca-LS and LSBP used at an optimum dosage can be effective stabilizing agents for immobilizing Cu and Pb in contaminated fine soils.

Resource utilization of ultrasonic carbonated MSWI fly ash as cement aggregates: Compressive strength, heavy metal immobilization, and environmental-economic analysis

Ultrasonic carbonation technology is effective for municipal solid waste incineration fly ash (MSWI FA) pretreatment. However, the subsequent disposal route is unclear. In this study, the mechanical strength and heavy metal immobilization effects of raw FA (RFA), washed FA (WFA), conventional carbonated FA (CFA), and ultrasonic carbonated FA (UFA) as cement aggregates in the preparation of concrete were investigated in comparison. The reaction kinetic analysis showed that ultrasonic excitation promoted the internal diffusion phase of the carbonation reaction. The compressive strength of the 28-day solidified bodies was in the order of UFA (32.2 MPa) > CFA (22.8 MPa) > WFA (16.4 MPa) > RFA (12.6 MPa). The 3-day UFA solidified body showed the highest degree of hydration and polymerization through 29Si solid-nuclear-magnetic analysis. The nano-CaCO3 in the UFA provided more nucleation sites and hydration reaction sites for the hydration reaction. In addition, the fine UFA particles filled the pores between cement particles, enhancing the strength of the product. Heavy metal leaching tests described that CFA and UFA met the criteria for resource utilization (HJ/T 1134–2020), and the immobilization efficiency of Cu, Pb, and Zn in the UFA solidified body was above 95.6%, 99.3%, and 99.2%, respectively, mainly by the dual immobilization of carbonate chemical precipitation and cement hydration. Considering 11 environmental impact factors and economic benefits, life-cycle-assessment and cost-benefit analysis were selected. The integrated environmental-economic results show that cement usage is the main influencing factor. UFA scenario was recommended as engineering applications with low global warming potential.

Carbonate-activated binder modified by supplementary materials for mine backfill and the associated heavy metal immobilization effects

Carbonate-activated binder modified by supplementary materials for mine backfill and the associated heavy metal immobilization effects

Effects of chemical composition on lightweight aggregates produced from contaminated soil: Phase regulation, immobilization mechanism and leaching prediction

Contaminated soil induces serious environmental risk due to the presence of hazardous components. The preparation of lightweight aggregate (LWA) is a widely accepted technique to treat contaminated soil. This study investigated the effect of contaminated soil composition on the physical properties and immobilization of heavy metals (Cu, Cr, Pb and Ni) of LWA. Phase regulation, immobilization mechanism and leaching prediction of LWA were analyzed. Results showed that SiO2 and Al2O3 were detrimental to the bloating performance of LWA, whereas fluxing components (Fe2O3, Na2O, K2O, CaO, and MgO) are all conducive. Fluxing components can bring more liquid phase, resulting in a lower density of LWA. The addition of Fe2O3 facilitated the immobilizing Cu and Cr owing to the formation of spinel phases, such as (Mg,Cu)(Fe,Ni)2O4 and Fe(Cr,Al)2O4. Glassy phase could encapsulate heavy metals remarkably, while the high content of fluxing components was unfavorable to the immobilization of Cu and Ni. As network modifiers, Cu and Ni could participate in the formation process of glassy phase, and get encapsulated by liquid phase from fluxing components. Based on the leaching results of Cu, Cr, Pb, and Ni, leaching prediction of LWA was conducted by characteristic indexes and Riley's phase diagram. This research could guide the manufacturing process and leaching control of LWA recovered from contaminated soil.

Effects of biochar and zero valent iron on the bioavailability and potential toxicity of heavy metals in contaminated soil at the field scale

Heavy metals (HMs) such as copper, nickel and chromium are toxic, so soil contaminated with these metals is of great concern. In situ HM immobilization by adding amendments can decrease the risk of contaminants being released. A five-month field-scale study was performed to assess how different doses of biochar and zero valent iron (ZVI) affect HM bioavailability, mobility, and toxicity in contaminated soil. The bioavailabilities of HMs were determined and ecotoxicological assays were performed. Adding 5 % biochar, 10 % ZVI, 2 % biochar + 1 % ZVI, and 5 % biochar + 10 % ZVI to soil decreased Cu, Ni and Cr bioavailability. Metals were most effectively immobilized by adding 5 % biochar + 10 % ZVI, and the extractable Cu, Ni, and Cr contents were 60.9 %, 66.1 % and 38.9 % lower, respectively, for soil with 5 % biochar + 10 % ZVI added than unamended soil. The extractable Cu, Ni, and Cr contents were 64.2 %, 59.7 % and 16.7 % lower, respectively, for soil with 2 % biochar + 1 % ZVI added than unamended soil. Experiments using wheat, pak choi and beet seedlings were performed to assess the remediated soil toxicity. Growth was markedly inhibited in seedlings grown in extracts of soil with 5 % biochar, 10 % ZVI, or 5 % biochar + 10 % ZVI added. More growth occurred in wheat and beet seedlings after 2 % biochar + 1 % ZVI treatment than the control, possibly because 2 % biochar + 1 % ZVI simultaneously decreased the extractable HM content and increased the soluble nutrient (carbon and Fe) content of the soil. A comprehensive risk assessment indicated that adding 2 % biochar + 1 % ZVI gave optimal remediation at the field scale. Using ecotoxicological methods and determining the bioavailabilities of HMs can allow remediation methods to be identified to efficiently and cost-effectively decrease the risks posed by multiple metals in soil at contaminated sites.

Effect of Grain Size Distribution of Soil on Immobilization of Cadmium and Nickel in Contaminated Soil Using Nano Zerovalent Iron: A Factorial Design and Response Surface Methodology Approach

Urban soils get contaminated due to the unscientific disposal of industrial effluents and solid waste, contaminating the soil with heavy metals. Contaminated soils need to be remediated to avoid the ingestion of toxic heavy metals. The immobilization of heavy metals is one of the methods to remediate contaminated soils. The primary purpose of this study was to explore the effect of grain size distribution (GSD) of soil on the efficiency of immobilization of toxic heavy metals in soil when nano zerovalent iron (nZVI) is used to immobilize the metals. Preliminary studies conducted with the 23 factorial design method confirmed that GSD is a significant factor along with the level of contamination and nZVI dosage in the immobilization of heavy metals in soil. Experiments were conducted with cadmium (Cd) and nickel (Ni), the toxic heavy metals, and three soils with different finer particles than 75 µm. Immobilization efficiency was obtained by comparing the leachability of contaminated and treated soil samples using the toxicity characteristic leaching procedure. Reduction in available fraction and variation in the speciation of heavy metals was observed through the sequential extraction procedure. The response surface methodology was adopted for analysis with three levels of GSD, contamination, and nZVI dosage. For Cd, a reduced cubic model was the best fit with a coefficient of determination (R-square) of 0.93, and for Ni, a quadratic model was the best fit with an R-square of 0.92. Both these models were validated experimentally. The efficiency variation followed an optimum curve concerning GSD, contamination level, and the nZVI dosage. For multimetal contamination, the immobilization efficiency gradually decreased from 10% finer to 90% finer soil, both in the case of Cd and Ni. It was observed that for both single metal and multimetal contamination, the interaction between soil and the nZVI plays a vital role in immobilization along with the factors considered.

Simultaneous immobilization of heavy metals and nutrient elements in contaminated sediment using a novel composite agent product.

In this research, an innovative type of sediment resource treatment agent (SRA) was synthesized successfully, which could immobilize ammonia nitrogen (NH3-N), total phosphorus (TP), potassium (K), and simultaneously stabilize cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn) in dredged sediment. The effects of SRA dosage on stabilizing the nutrient elements and heavy metals were investigated. The results demonstrated that the increase of SRA dosage significantly enhanced the stabilization of nutrients and heavy metals. The 14-day rainwater infiltration and rainwater scouring experiments were carried out. With the simulation test of rainwater infiltration, the stabilization ratios of Cr, Cu, Ni, Pb, Zn, Cd, NH3-N, TP, and K with 2% SRA addition reached 80.8%, 76.8%, 80.3%, 77.5%, 78.0%, 72.7%, 64.3%, 73.9%, and 73.9%, respectively. Under the action of rainwater scouring, the stabilization ratios of Cr, Cu, Ni, Pb, Zn, Cd, NH3-N, TP, and K with 6.4% SRA addition reached 84.6%, 84.0%, 77.6%, 87.3%, 80.0%, 61.5%, 76.2%, 77.8%, and 91.7%, respectively. Therefore, the results demonstrate that SRA is an excellent composite material in stabilizing heavy metals while reserving the nutrients in dredged sediment, thus showing great potential in the application for dredged sediment resource treatment.

Reduction of bioavailability and phytotoxicity effect of cadmium in soil by microbial-induced carbonate precipitation using metabolites of ureolytic bacterium Ochrobactrum sp. POC9.

The application of ureolytic bacteria for bioremediation of soil contaminated with heavy metals, including cadmium (Cd), allows for the efficient immobilization of heavy metals by precipitation or coprecipitation with carbonates. Microbially-induced carbonate precipitation process may be useful also in the case of the cultivation of crop plants in various agricultural soils with trace but legally permissible Cd concentrations, which may be still uptaken by plants. This study aimed to investigate the influence of soil supplementation with metabolites containing carbonates (MCC) produced by the ureolytic bacterium Ochrobactrum sp. POC9 on the Cd mobility in the soil as well as on the Cd uptake efficiency and general condition of crop plants (Petroselinum crispum). In the frame of the conducted studies (i) carbonate productivity of the POC9 strain, (ii) the efficiency of Cd immobilization in soil supplemented with MCC, (iii) crystallization of cadmium carbonate in the soil enriched with MCC, (iv) the effect of MCC on the physico-chemical and microbiological properties of soil, and (v) the effect of changes in soil properties on the morphology, growth rate, and Cd-uptake efficiency of crop plants were investigated. The experiments were conducted in soil contaminated with a low concentration of Cd to simulate the natural environmental conditions. Soil supplementation with MCC significantly reduced the bioavailability of Cd in soil with regard to control variants by about 27-65% (depending on the volume of MCC) and reduced the Cd uptake by plants by about 86% and 74% in shoots and roots, respectively. Furthermore, due to the decrease in soil toxicity and improvement of soil nutrition with other metabolites produced during the urea degradation (MCC), some microbiological properties of soil (quantity and activity of soil microorganisms), as well as the general condition of plants, were also significantly improved. Soil supplementation with MCC enabled efficient Cd stabilization and significantly reduced its toxicity for soil microbiota and plants. Thus, MCC produced by POC9 strain may be used not only as an effective Cd immobilizer in soil but also as a microbe and plant stimulators.

Modified Natural Diatomite with Various Additives and Its Environmental Potential.

Diatomite has recently been the subject of intensive scientific research aimed at its extensive use in industry, breeding and agriculture. The only active diatomite mine is in Jawornik Ruski, in the Podkarpacie region of Poland. Chemical pollution in the environment, including that from heavy metals, poses a threat to living organisms. Reducing the mobility of heavy metals in the environment through the use of diatomite (DT) has recently gained much interest. More effective immobilisation of heavy metals in the environment with DT, mainly through the modification of its physical and chemical properties by various methods, should be applied. The aim of this research was to develop a simple and inexpensive material showing more favourable chemical and physical properties compared with unenriched DT in terms of metal immobilisation. Diatomite (DT), after calcination, was used in the study, considering three grain fractions, i.e., 0-1 mm (DT1); 0-0.5 mm (DT2) and 5-100 µm (DT3). Biochar (BC), dolomite (DL) and bentonite (BN) were used as additives. The proportion of DTs in the mixtures amounted to 75%, and of the additive, 25%. The use of unenriched DTs after calcination poses the risk of releasing heavy metals into the environment. Enrichment of the DTs with BC and DL resulted in a reduction or absence of Cd, Zn, Pb and Ni in aqueous extracts. It was found that for the specific surface area values obtained, the additive used for the DTs was of crucial importance. The reduction in DT toxicity has been proven under the influence of various additives. The mixtures of the DTs with DL and BN had the least toxicity. The obtained results have economic importance, as the production of the best quality sorbents from locally available raw materials reduces transport costs and thus the environmental impact. In addition, the production of highly efficient sorbents reduces the consumption of critical raw materials. It is estimated that the savings from producing sorbents with the parameters described in the article can be significant in comparison with popular competitive materials of other origins.

Utilization of size-fractionated pozzolanic bottom ash to immobilize heavy metals in MSW incinerator fly ash

Fly ash (FA) from Municipal solid waste incineration (MSWI) is disposed of in landfills after the immobilization of hazardous heavy metals. Pozzolans found in the fine-fraction of MSWI bottom ash (BA) have the potential to immobilize heavy metals. The aim of this study was to examine the effect of size-fractionated BA in immobilizing heavy metals in FA, in order to enhance the effective utilization of resources. BA was applied at two distinct fractions (d<0.25 and d<2.0 mm) when considerable amorphous reactive pozzolans (i.e., siliceous and aluminous) were present. In order to conduct the experiments, FA, BA, and water were mixed in a ratio of 10:1:10, dried at room temperature and in an oven at 120 °C for 4 h, and settled for 4, 8, 16, 30, and 60 days. The results showed that under the air-dried conditions, both BA fractions significantly immobilized Pb and Zn. Pb and Zn leaching stabilized at about 99.9% and 95.6%, respectively, over 16 days with a BA fraction of d< 0.25 mm in an air-dry environment. The pH reduction, the calcite, C-S-H gel, and several new secondary minerals formation demonstrated that the carbonation and pozzolanic reactions were the immobilization mechanisms. Despite the method's simplicity, the findings suggested a potential approach of utilizing residual BA fractions that can be reused directly in the incineration facility. Therefore, this technique can minimize the amount of raw materials required as a metal stabilizer, reduce the amount of waste sent to landfills, and create a new material that can be reused as fillers.