Sequential Extraction Tests Research Articles

Enhanced removal of Fe, Cu, Ni, Pb, and Zn from acid mine drainage using food waste compost and its mechanisms

Heavy metals (HMs) in acid mine drainage (AMD) pose serious threats to aquatic life and soil. Biosorbents are promising materials to remove HMs from wastewater. Herein, food waste compost was used as a low-cost and sustainable biosorbent to remove Fe3+, Cu2+, Ni2+, Pb2+, and Zn2+ from an AMD and other model solutions with an initial pH of 2.24. Batch adsorption tests were conducted to systematically investigate the influences of initial pH, compost dose, the presence of Fe3+ and SO42− ions, and the pH-induced Fe precipitates on the removal performance. The involved removal mechanisms were explored by conducting stepwise precipitation tests, sequential extraction tests, and Fourier transform infrared spectroscopy (FTIR) characterization. It was found that the addition of the compost removed over 90% of Zn, Ni, Cu, and Pb at pH 5.80, 5.50, 4.50, and 3.00, respectively. At low compost doses, the presence of Fe3+ and SO42− ions hindered the removal since the competition effect of Fe3+ ion and lower absorbability of metal-sulfate complexes, respectively. Sequential extraction tests revealed that higher fractions of Fe, Cu, and Pb were strongly immobilized through complexation and precipitation relative to Ni and Zn. Additionally, the pH-induced Fe precipitates did not favor the removal of the HMs, probably due to the adsorption of organic components released from the compost. This study suggests that compost have the potential to remove HMs from acidic wastewater without pre-neutralization.

Solidification and stabilization of heavy metals in medical waste ash through alkali activation

In the present work, medical waste ash was used as an aluminosilicate precursor to produce a geopolymer binder with stabilised heavy metals. The ash was initially calcined at a temperature of 800 °C for two hours to reduce the organic content. Calcined kaolin and medical waste ash were used as precursors to produce the geopolymer binder and sodium silicate and calcium oxides were used as alkaline activators. The effect of curing temperature (23, 60, and 100 °C) and the calcium oxide addition (0, 5, and 10%) on the geopolymer properties were evaluated. Eighteen geopolymer samples were prepared and evaluated for immobilizing heavy metals through the Toxicity Characteristic Leaching Procedure (TCLP). When compared to raw materials, TCLP results indicated that geopolymerization can significantly reduce the concentration of heavy metals in the medical waste ash leachate. The metal fixation percentages of the geopolymers ranged from 70 to 100%. The sequential extraction test results showed that geopolymerization (stabilization/solidification) is very beneficial in reducing the bioavailable fraction in the solid waste and maximizing the difficulty of fraction extraction.

Enhancing Lead Passivation in Contaminated Soil: Impacts of the Chemical Modification of Oxygen-Containing Groups (OCGs) on the Surface of Hydrochar

ABSTRACT In this study, we selected walnut shell-derived pristine HC (pHC) and two modified derivatives obtained by oxidative and alkali treatments (designated mHC-O and mHC-A, respectively) to investigate the passivation performance of Pb(II) in contaminated soil. The yields of mHC-A and mHC-O were 70.58% and 95.38%, respectively, after posttreatment. According to the XPS, FTIR, and acidity titration results, the amounts of the three major OCGs (i.e. C−O, C=O, and O−C=O) all increased after H2O2 oxidation. Moreover, chemical modification fundamentally changed the structural characteristics of pHC. DTPA extraction tests indicated that the extractable Pb content after 30 days of incubation decreased by 13.60%, 19.32% and 14.53% at 7% (w/w) doses of HC, mHC-O and mHC-A, respectively, compared to that of the control. Furthermore, mHC-O was superior to pHC and mHC-A in terms of Pb passivation efficiency, which was consistent with the results of BCR sequential extraction and leaching tests using three root exudates. For mHC-O at the 7% dose, the contents of bioavailable Pb in the contaminated soil were 19.85 and 8.83 mg/kg based on DTPA leaching and BCR analysis, respectively, while they were 0.616, 0.564 and 0.07 mg/kg in the root exudate leaching tests of Ophiopogon japonicus, radish and spinach, respectively, indicating that the root exudate leaching method lowered the bioavailable Pb content compared to the DTPA and BCR methods. Overall, Oxidation posttreatment with HC could improve the passivation of Pb in contaminated soils.

Study on modes of occurrence and selective leaching of lithium in coal gangue via grinding-thermal activation

Lithium (Li), an important strategic metal, has been paid attention to by researchers, entrepreneurs, and political circles, especially its recovery from coal-based solid waste. In this paper, the occurrence modes of Li in coal gangue (CG) have been studied through sequential chemical extraction, distribution correlation, and intercalation-leaching test. The CG was pretreated via grinding-thermal activation to selectively leach Li. The correlation between Li and magnesium (Mg) during the leaching process was also investigated. Finally, the migration mechanism of Li during the grinding-thermal activation process was analyzed using solid-state nuclear magnetic resonance for the first time. The results of the first three experiments demonstrated that Li primarily exists within the kaolinite. The extraction of Li from CG after grinding-thermal activation is 44.82 % using 0.2 M (NH4)2SO4 (pH = 4.0), while aluminum (Al) was almost insoluble, exhibiting the selective leaching of Li. 84.76 % of Li and 17.63 % of Al are obtained at pH = 1.0. The correlation analysis result suggests that lithium ions (Li+) exist in the octahedron of the lattice as charge compensation. The migration mechanism is explained by the chemical shift of Li+, which moves from −0.196 ppm (raw, in the octahedron) to −0.319 ppm (ground, octahedral destruction) and further to −0.564 ppm (thermal activation, out of the octahedron). This paper can provide a theoretical basis for the occurrence of Li and a new method for selective extraction of Li from CG.

Co-treatment of steel slag and oil shale waste in cemented paste backfill: Evaluation of fresh properties, microstructure, and heavy metals immobilization

The environmentally sustainable treatment of steel slag (SS) and oil shale waste (OSW) is a significant concern in the field of industrial development. The mining industry also faces challenges related to the high costs and carbon emissions associated with ordinary Portland cement (OPC), leading to environmental pollution. To address these challenges, this study aimed to develop a cost-effective and environmentally friendly binder for cemented paste backfill (CPB) by utilizing SS and calcined oil shale waste (COSW) as primary precursors. Extensive investigations were conducted to evaluate the properties of the CPB sample with varying COSW content, including rheological properties, mechanical strength, and microstructure. The binder sample was comprehensively characterized using isothermal calorimetric analysis, X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy (SEM). Based on systematic experimentation, an optimal blend ratio for the binder was determined, consisting of 60 wt% SS, 15 wt% COSW, 15 wt% phosphogypsum (PG), and 10 wt% OPC. The exceptional performance of the binder was attributed to the substantial formation of precipitated ettringite (AFt), resulting in a more compact structure and improved mechanical strength. Additionally, a sequential extraction test revealed that the heavy metals in the CPB sample were mainly present in the residual fraction, demonstrating the effective immobilization of heavy metals by the binder.

Environmental risk assessment of the contamination of river water and sediments from the Bor mining area, East Serbia―Secondary Cu enrichment at the reservoir site

AbstractThe study area is within the Bor copper mining region, Eastern Serbia, where wastewaters from the Bor metallurgical/smelting facilities have caused serious copper (Cu) and arsenic (As) contamination to the Timok river system. The operating conditions at smelting facilities control the pH of the river waters, resulting in highly acidic waters in 2019 than 2015. This study compares the mobility of Cu and As and risk assessment of river water contamination during both years as well as assessing the risks of riverbed sediments contamination and investigating the origins of Cu and As pollution. In the river system, As generally existed as a particulate species in the entire study area during both years and was widely removed from river waters by sorption onto the hydrous ferric oxides (HFO), whereas dissolved Cu was removed from river waters only at neutral pH conditions with hydrous aluminum oxides (HAO) and HFO at the downstream reservoir site of Timok River. Despite the similarity in Cu mobility during both years, the lower pH of river waters in 2019 than 2015 enabled dissolved Cu species to be transported farther downstream, resulting in a higher level of river water pollution. The contamination factor (CF), used to estimate levels of sediment pollution, had higher values for Cu and As compared to Zn, Pb, Co, and Ni. The CF values of Cu were the highest in sediments near the Bor metallurgical/smelting facilities and at downstream reservoir site, whereas the CF values of As were generally high in the entire research field. Additionally, the ecological risk potential (Er) values of Cu were the highest in sediments of the Bor River and Timok River, reflecting an enrichment of Cu at these sites. Finally, a clarification on the origin of Cu pollution and risks of mobilization was inferred from the sequential extraction test. The predominant Cu species in sediments of the upstream region were oxidizable and residual, hosted by copper sulfides originating from the flotation tailings, suggesting a relatively low risk of Cu release from these sediments. However, at the downstream site (especially reservoir sediments), the contribution of acid‐soluble Cu was 34.8%, suggesting a higher risk of Cu release. The highest contributions of acid‐soluble and reducible Cu (18%) at the reservoir site were promoted by the effective settlement of Cu‐sorbing HAO and HFO. The Cu contents of these two fractions were 0.86 wt%, almost three times higher than that of Cu ore in Veliki Krivelj open pit mine.

Geochemical controls on mobilization of metals from a 100-year-old waste rock pile and implications for selection of cover amendments

Reclamation of mine waste rock piles typically consists of constructing a cover with amendments to improve conditions for vegetation. However, cover amendments have potential to mobilize metals in waste by introducing new chemicals and altering pH and redox conditions. This study evaluates metal phases in a 100-year-old waste rock pile with high metals content (3.5% lead by weight, 0.8% zinc, and 0.75% copper) and the potential for these metals to be mobilized by several cover materials and amendments (topsoil, spent brewery grain, biochar, compost, commercial soil media, and phosphate). Laboratory testing indicates that metals have weathered from their initial metal sulfide phases (galena, sphalerite, chalcopyrite), and are now also present as sulfates, phosphates, carbonates, and phases associated with manganese/iron oxides. Sequential extraction tests demonstrated that the largest extractable fraction of metals is associated with manganese/iron oxides (37% of lead by weight, 22% of copper, and 26% of zinc), suggesting an environmental risk should geochemically reducing conditions develop and mobilize metals in the pile after cover construction. Testing of specific cover materials demonstrated that metals mobilization also occurs from low pH (as with spent brewery grain), formation of stable aqueous metal–organic complexes (as with spent brewery grain and compost), and ligand exchange (as with phosphate amendment). Results of this study demonstrate the importance of identifying metal phases present in a waste rock pile prior to selecting cover amendments.

The Effect of Physical Separation and Calcination on Enrichment and Recovery of Critical Elements from Coal Gangue

Critical metallic elements in coal gangue have great utilization potential, especially due to the current shortage of these metals. This paper focused on examining the feasibility of physical separation (screening and float-sink tests) and calcination treatment for the enrichment of critical elements (Li, Ga, and rare earth elements plus yttrium (REY)) from coal gangue. The impacts of these enrichment methods on the acid leaching recovery of these elements were then studied. Screening tests indicated that Li and Ga were enriched in >0.125 mm size fraction and the content of REY was highest in <75 μm size fraction. Float-sink tests showed that high-density fractions were enriched in Li and Ga, and low-density fractions were enriched in REY. Physical separation cannot significantly improve the leaching rate of Li, Ga, and REY. Notably, Li, Ga, and REY were enriched significantly, and their acid leaching recoveries were increased by 54~68% after calcination under 400 °C. Sequential chemical extraction tests showed that the majority of insoluble Li, Ga, and REY was converted into soluble forms at the above temperature, which is attributed to the formation of amorphous metakaolinite and the decomposition of organic matter. Based on the results, a conceptually combined flowsheet was proposed for the extraction of Li and Ga from coal gangue.

Effects of calcination temperature on the occurrence modes of rare earth elements in coal

Prior research confirmed that acid leaching recovery of rare earth elements (REEs) from coal was significantly enhanced by calcination pretreatment. To better understand the positive effect, sequential chemical extraction tests were performed in this study on raw and calcined coals of the Western Kentucky No. 13 and Fire Clay seams. The effects of calcination temperature on the occurrence modes of REEs and other selected elements in the calcination products were evaluated. Correlations between distributions of the REEs and major elements in different occurrence modes were established. Experimental results indicated that reactions such as organic matter oxidization, clay dehydration, phosphate mineral decomposition, aluminum silicate fusion, and iron oxide aggregation occurred during the calcination process and collectively determined the occurrence modes of REEs. Findings from the study will contribute to REE recovery and comprehensive utilization of coal.

Water-Rock Interaction Processes: A Local Scale Study on Arsenic Sources and Release Mechanisms from a Volcanic Rock Matrix.

Arsenic is a potentially toxic element (PTE) that is widely present in groundwater, with concentrations often exceeding the WHO drinking water guideline value (10.0 μg/L), entailing a prominent risk to human health due to long-term exposure. We investigated its origin in groundwater in a study area located north of Rome (Italy) in a volcanic-sedimentary aquifer. Some possible mineralogical sources and main mechanisms governing As mobilization from a representative volcanic tuff have been investigated via laboratory experiments, such as selective sequential extraction and dissolution tests mimicking different release conditions. Arsenic in groundwater ranges from 0.2 to 50.6 μg/L. It does not exhibit a defined spatial distribution, and it shows positive correlations with other PTEs typical of a volcanic environment, such as F, U, and V. Various potential As-bearing phases, such as zeolites, iron oxyhydroxides, calcite, and pyrite are present in the tuff samples. Arsenic in the rocks shows concentrations in the range of 17–41 mg/kg and is mostly associated with a minor fraction of the rock constituted by FeOOH, in particular, low crystalline, containing up to 70% of total As. Secondary fractions include specifically adsorbed As, As-coprecipitated or bound to calcite and linked to sulfides. Results show that As in groundwater mainly originates from water-rock interaction processes. The release of As into groundwater most likely occurs through desorption phenomena in the presence of specific exchangers and, although locally, via the reductive dissolution of Fe oxy-hydroxides.

Modification of carbonate-activated binder for lead-zinc mine tailings based cemented paste backfill

CPB promotes a green development of the mining industry. At the same time, the high cost of OPC limits the large-scale application of CPB. This study aimed to use carbonate-activated binders as cementitious materials in LZT based CPB. The binder was modified by CLDH and/or HM when considering the carbonate-activated binder's low reaction rate and bad performance. The effect of 3–5 wt% CLDH and 0.5–1 wt% HM on the reaction kinetics and phase assembles of Na2CO3-activated slag was investigated via isothermal calorimetry, XRD, and TG analysis. Flowability, setting time, and compressive strength of CPB samples were used to assess the feasibility of the binder in CPB. The immobilization effect and leaching mechanism of heavy metals from the CPB samples were then evaluated via TCLP, sequential extraction test, and semi-dynamic leaching. The incorporation of CLDH and HM accelerated binder reaction through consuming CO32−. The coupling addition of 3 wt% CLDH and 0.5 HM presented the best performance, reaching about 2.29 MPa at 28 days. This value was higher than OPC-based CPB samples by around 10%.

Preparing a binder for cemented paste backfill using low-aluminum slag and hazardous oil shale residue and the heavy metals immobilization effects

The high cost and carbon emission of ordinary Portland cement (OPC) increase the burden of mining industry and aggravate environmental pollution. In this study, a cheaper and greener binder was prepared using low-aluminum slag and calcined oil shale residue (COSR) as main precursors to provide an alternative cementing material for cemented paste backfill (CPB). The influence of COSR content on the properties of the CPB sample was investigated, including rheological properties, setting time, mechanical strength, and pore structure. Characterization of binder sample was then conducted via isothermal calorimetric analysis, X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscope (SEM). The optimal mix proportion of binder was 56 wt% slag, 24 wt% COSR, 15 wt% flue gas desulfurization gypsum (FGDG), and 5 wt% OPC. The solid waste utilization rate in the binder production reached 95%, considered an eco-friendly binder. Besides, the best performance of the binder was mainly due to the optimal Al2O3 and CaO content, leading to large amounts of precipitated ettringite. It then contributed to a denser structure with high mechanical strength. Furthermore, the sequential extraction test showed that the heavy metal in the solidified CPB sample existed mainly as a residual fraction, contributing to the superior immobilization effects.

Comparison of limestone calcined clay cement and ordinary Portland cement for stabilization/solidification of Pb-Zn smelter residue.

Decreasing carbon emissions by replacing Portland cement (PC) with supplementary cementitious materials (SCMs), such as low-grade limestone (LS) and calcined clays (CC), has tremendous potential for stabilization/solidification (S/S) of industrial hazardous waste primarily with heavy metals. Recently, a low-carbon-based cementitious binder, namely, limestone calcined clay cement (LC), has emerged as an alternative for S/S treatment of wastes. However, comprehensive comparison between LC and PC application in solidifying/stabilizing wastes has not been conducted. This study aims to investigate the S/S efficiency of Pb-Zn smelter residue (LZSR) comprising heavy metals lead (Pb), zinc (Zn), and cadmium (Cd) at higher concentrations. LZSR is treated with LC and PC for capturing strength and leaching toxicity. The test results indicate that low-grade CC and LS in the LC binder can promote the alkaline environment, and act as fillers in solidifying heavy metals. The toxicity characteristic leaching procedure leaching concentrations of untreated (UT) LZSR were 503 mg/kg, 1266 mg/kg, and 251 mg/kg for Pb, Zn, and Cd, respectively. After a 28-day curing, the leaching concentrations in LC-treated LZSR reduced to 4.33 mg/kg, 189.68 mg/kg, and 0.46 mg/kg, while the leaching concentrations of PC-treated LZSR reduced to 29 mg/kg, 338 mg/kg, and 6 mg/kg for Pb, Zn, and Cd, respectively. The maximum immobilization efficiencies for Pb, Zn, and Cd reached 85%, 99%, and 99%, respectively. Moreover, the insoluble phases for Pb, Zn, and Cd obtained from the sequential extraction test results were 63.5%, 72.1%, and 42.4% for LC-treated LZSR and 35.7%, 38%, and 43% for PC-treated LZSR with binder content of 8% binder and curing time of 28 days. Increasing curing time and binder content reduced leaching concentrations, and the underneath mechanisms were interpreted by XRD, SEM-EDS, and FTIR analyses. Overall, the results indicate that Pb, Zn, and Cd can be successfully immobilized using 8% LC binder by transforming soluble heavy metals to insoluble hydroxides and their complexes.

Enhanced leaching recovery of rare earth elements from a phosphatic waste clay through calcination pretreatment

Phosphatic clay is a waste material produced during the beneficiation of phosphate ore, which likely poses severe environmental problems. In this study, a phosphatic clay containing 258 ppm of total rare earth elements (REEs) was used as a feedstock for REE recovery. By reacting with 0.1 M HCl at 75 °C for 3 h, around 36 % of light REEs and 65 % of heavy REEs were extracted from the raw material. However, after calcination pretreatment at 600 °C for 2 h, the recovery was increased to 73 % and 81 %, respectively, which are close to the recoveries obtained from the raw material using a much higher acid concentration of 1.2 M. Based on the findings from sequential chemical extraction tests and scanning electron microscopy analysis, the positive impact was explained by the decomposition and conversion of REE-bearing minerals into more leachable species. Using a higher calcination temperature of 900 °C, recovery of both the light and heavy REEs was largely reduced relative to the raw material. Mineralogical analyses showed that the dominant minerals existing in the material, such as muscovite, were fused and sintered during the calcination at 900 °C. These reactions likely caused the decreases in the recovery. The results and findings from this study will contribute to the beneficial uses of phosphatic clay and the production of REEs.

Chemical State Analysis of Heavy Metals and Radioactive Cesium in Municipal Solid Waste Incineration Fly Ash Contaminated with Radioactive Cesium Released by the FDNPP Accident.

The chemical states of heavy metals and radioactive Cs were estimated in fly ash sampled at Fukushima prefecture, Japan. Estimating the speciation of incinerator fly ash is important to ensure an appropriate and efficient management of fly ash generated from disaster-related waste. In this study, fly ash collected at a waste incineration facility in Fukushima prefecture was treated using a sequential extraction test. The test results indicated that the solubility behavior of radioactive Cs was similar to that of NaCl and KCl, and approximately 60% of radioactive Cs was included as water-soluble chloride compounds in the fly ash sample. Most heavy metals eluted in three fractions, in the extraction steps for carbonate-bound, free oxide, and bound to organic matter species. The chemical states of elements in the three non-water-soluble fractions and residue showed minimal elution into the environment. Therefore, most heavy metals in the fly ash exhibited minimal elution into the environment.

Speciation of rare earth elements in acid mine drainage precipitates by sequential extraction

Recent efforts have shown that acid mine drainage precipitates (AMDp) may be a promising source of rare earth elements and critical materials (REE/CM). To better understand this resource, several particle characterization studies were conducted on AMDp samples from three AMD treatment sites in Northern and Central Appalachia. This work included the determination of particle size, size distribution, morphology, mineralogy, chemical speciation, and rare earth content. While the particle characteristics and mineralogy varied considerably from site to site, sequential extraction tests showed that the largest portion of REEs (45% to 75%) were found in soluble phases bound to Fe-Mn oxides. Carbonates (5% to 16%) and insoluble residues (4% to 24%) were also found to be significant in some samples, suggesting that different AMD chemistry and AMD treatment approaches can lead to substantial variation in the deportment of REEs to the various chemical phases. Altogether, the results suggest that chemical extraction of REEs from AMDp can be achieved under mild conditions with high recovery values; however, the significant site-by-site variation will necessitate detailed testing of individual samples to determine the overall economic viability.

Partitioning of uranium in contaminated bottom sediments: The meaning of fractionation

Sequential extraction tests were used to study partitioning of U in the bottom sediments of two reservoirs that have been used for the temporary storage of nuclear waste at the “Mining and Chemical Combine” (Zheleznogorsk, Krasnoyarsk region, Russia). Various sequential extraction protocols were applied to the bottom sediment samples and the results compared with those obtained for laboratory-prepared simulated samples with different speciation and partitioning, e.g., U(VI) sorbed onto various inorganic minerals and organic matter, as well as uranium oxides. The distributions of uranium in fractions extracted from simulated and actual contaminated samples were compared to shed light on the speciation of U in the bottom sediments. X-ray absorption spectroscopy, X-ray diffraction, and scanning electron microscopy were also used to analyze the partitioning of U in contaminated sediments. We also compared the results obtained using the spectroscopic and microscopic techniques, as well as sequential extraction.

Highly efficient sorption and immobilization of gaseous arsenic from flue gas on MnO2/attapulgite composite with low secondary leaching risks

Some sorbents have been developed for arsenic (As) compounds capture from flue gas . However, most of the conventional sorbents have cost constraints and can cause secondary pollution due to the leaching of arsenic after use. To solve this problem, a new and highly efficient adsorbent for gaseous arsenic was successfully developed in this paper with excellent immobilization performance and low-cost. A series of Mn-supported attapulgite (ATP) composites were fabricated, characterized, and investigated for arsenic capture. The modification of ATP with Mn not only considerably enhanced the adsorption efficiency but also stabilized the adsorbed As in the spent sorbents. SO 2 in flue gas promoted the adsorption performance through As-sulfate binding, whereas NO was beneficial for the oxidation of As(III) to As(V) on the surface of Mn-modified ATP. The incorporation of Mn with ATP generated abundant hydroxylate (OH − ) from hydration and accelerated the formation of As-sulfate compounds, which was beneficial for physical encapsulation . The results of the toxicity characteristic leaching procedure and sequential extraction test revealed that adsorbed As could be considerably immobilized by the sorbent with low leaching ability. Mn modification changed more As into inert fractions and consequently inhibited release from spent sorbents, which considerably reduced the risks of secondary pollution. The developed composite can be potentially used as a new efficient sorbent for gaseous arsenic capture in flue gas. • Manganese modification effectively enhanced the capacity of ATP for gaseous arsenic removal in flue gas. • Trivalent arsenic was oxidized into pentavalent arsenic during the process. • Manganese oxides facilitated the transformation of adsorbed-arsenic on Mn-ATP from leachable fraction to inert fraction.

Chinese operator lets contract for PDH units

Some sorbents have been developed for arsenic (As) compounds capture from flue gas. However, most of the conventional sorbents have cost constraints and can cause secondary pollution due to the leaching of arsenic after use. To solve this problem, a new and highly efficient adsorbent for gaseous arsenic was successfully developed in this paper with excellent immobilization performance and low-cost. A series of Mn-supported attapulgite (ATP) composites were fabricated, characterized, and investigated for arsenic capture. The modification of ATP with Mn not only considerably enhanced the adsorption efficiency but also stabilized the adsorbed As in the spent sorbents. SO2 in flue gas promoted the adsorption performance through As-sulfate binding, whereas NO was beneficial for the oxidation of As(III) to As(V) on the surface of Mn-modified ATP. The incorporation of Mn with ATP generated abundant hydroxylate (OH−) from hydration and accelerated the formation of As-sulfate compounds, which was beneficial for physical encapsulation. The results of the toxicity characteristic leaching procedure and sequential extraction test revealed that adsorbed As could be considerably immobilized by the sorbent with low leaching ability. Mn modification changed more As into inert fractions and consequently inhibited release from spent sorbents, which considerably reduced the risks of secondary pollution. The developed composite can be potentially used as a new efficient sorbent for gaseous arsenic capture in flue gas.

The evaluation of immobilization behavior and potential ecological risk of heavy metals in bio-char with different alkaline activation.

The bio-char was prepared by co-pyrolysis of municipal sewage sludge and biomass with chemical activation. The alkaline activating agents of KOH and K2CO3 were used to develop multilevel pore structure without heavy metal. The proximate analysis, ultimate analysis, SEM, and surface area and porosity analyzer were applied to present the physico-chemical properties and multilevel pore structure of bio-char. After impregnation pretreatment, the KOH provided more functional ingredients and reacted with C to expand pore structure for bio-chars. It was confirmed the specific surface area reached 2122.43 m2/g, and micropore area was 1674.85 m2/g after co-pyrolysis at 800 °C. Through the pretreatment of alkaline activation, the novel evaluation of heavy metal immobilization behavior in bio-char matrix were investigated by BCR sequential extraction and leaching tests. The KOH activation showed prominent immobilization behavior relatively, and the K2CO3 activation had more noticeable effects on leaching behavior. For Cu, Ni, Cr, Cd, Pb, and Zn, after co-pyrolysis at 900 °C, the proportion of unstable fraction decreased significantly, and the residual fractions of heavy metals were above 89.44% according to BCR sequential extraction procedure. Under optimal pyrolysis temperature, the Er value of bio-char reduced to 41.93, and the potential ecological risks decreased from considerable risk to low risk to ensure the further eco-friendly application.