•Humic acid residue (HAS) is currently a wasted resource.•We modified HAS with NH4H2PO4 to improve its heavy metal stabilization capacity.•N-HAS reduces the mobility of Hg and Pb in soils.•Addition ...of N-HAS alters soil physicochemical properties.•N-HAS was an industrially produced heavy metal passivator.
Humic acid residue (HAS), as a waste product from the extraction of humic acid from low-rank coal such as weathered coal and lignite, is characterized by its abundant yield and low price. However, the low efficiency and high pH value of HAS in passivating heavy metals limit their application in the passivation of heavy metals in soils. To improve the passivation efficiency of humic acid residues against heavy metals, in this study, modified humic acid residues (N-HAS) were prepared by pretreatment with HNO3 and modification with NH4H2PO4. The results showed that the passivation efficiency of N-HAS was up to 87.75% and 57.07% for Hg and Pb in the effective state, and the adsorption kinetics were under the pseudo-second-order model. The addition of N-HAS to the soil resulted in a change in the morphology of the heavy metals, with the acid extractable state of Hg and Pb reduced by 66.92% and 30.44% respectively, and the results of the Toxicity Leaching Test (TCLP) showed that the addition of N-HAS significantly reduced the leaching toxicity and potential ecological risk index (RI). The soil physicochemical properties changed after the addition of N-HAS and there was a correlation between the soil physicochemical properties and the effective state of Hg and Pb content. In conclusion, N-HAS has a positive effect on the remediation of heavy metal-contaminated soil and has a broad application prospect.
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•The bioremediation applications of co-contaminated soils with metals and pesticides were reviewed.•Factors affecting bioremediation of heavy metals and pesticides were discussed.•The ...bioremediation mechanisms and effectiveness evaluation methods of co-contaminated soil were introduced.•Potential research needs for this field were proposed.
Soil co-contaminated with heavy metals and pesticides has caused large global environmental issues. The interaction of heavy metals and pesticides make the contamination situation more complicated. It is crucial to remediate the co-contaminated soil by heavy metals and pesticides. Bioremediation has the advantages of high efficiency (especially for large, low contamination areas), low cost, easy available, harmless for the ecosystem and high public acceptance, which has been widely developed in remediation of combined pollution of heavy metals and pesticides. This paper reviews the bioremediation applications of combined contaminated soil with heavy metals and pesticides. Abiotic and biotic factors (e.g. pH, temperature, bioavailability of pollutants, the interactions between pollutants, biological competitiveness and biological state) can all affect the bioremediation of heavy metals and pesticides. Meanwhile, the present review summarizes the bioremediation mechanisms of heavy metals and pesticides by microorganisms and plants. The effectiveness evaluation methods of soil remediation are also reviewed. Based on above, this review proposes the future investigations required for this field.
Clay sediment is removed by dredging, resulting in the disposal of enormous waste sediment clay slurries that consumes land space, as well as risks the human health and the environment. Manganese ...(Mn) is often identified in clay slurries. Quicklime (CaO)-activated ground granulated blast-furnace slag (GGBS) can be used to stabilize/solidify (S/S) contaminated soils; nevertheless, few studies have been published on the S/S of Mn-contaminated clay slurries using CaO-GGBS. Moreover, the anions contained in clay slurries may affect the S/S efficiency of CaO-GGBS in treating Mn-contaminated clay slurries, but this effect has hardly been investigated. Therefore, this study investigated the S/S efficiency of CaO-GGBS in treating MnSO4-bearing and Mn(NO3)2-bearing clay slurries. The effect of anions (i.e. SO42− and NO3−) on the strength, leachability, mineralogy, and microstructure of Mn-contaminated clay slurries treated with CaO-GGBS was explored. Results showed that CaO-GGBS could improve the strength of both Mn-contaminated slurries to meet the strength requirement for landfill waste outlined by United States Environmental Protection Agency (USEPA). The Mn leachabilities of both Mn-contaminated slurries were decreased to be less than the Euro limit for drinking water after cured for 56 days. The MnSO4-bearing slurry generally produced higher UCS while lower Mn leachability than Mn(NO3)2-bearing slurry at the same CaO-GGBS addition. CSH and Mn(OH)2 were formed, thereby enhancing strength and reducing leachability of Mn. Ettringite in CaO-GGBS-treated MnSO4-bearing slurry, which was formed by the supply of SO42− from MnSO4, further contributed to the strength enhancement and the decrease of Mn leachability. Ettringite was the factor leading to the difference in strength and leaching properties between MnSO4-bearing and Mn(NO3)2-bearing clay slurries. Hence, anions contained in Mn-contaminated slurries significantly affected the strength and the Mn leachability, and need to be identified before CaO-GGBS was used to treat such slurries.
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•Anions in Mn-contaminated slurries affected strength and Mn leachability.•CaO-GGBS improved strength and leachability of Mn-contaminated slurries.•MnSO4-slurry had higher strength and lower Mn leachability than Mn(NO3)2-slurry.•Ettringite caused difference in properties between MnSO4- and Mn(NO3)2-slurries.
Utilizing solid waste-based binder to solidify/stabilize (S/S) heavy metal contaminated soils is a sustainable approach. This paper implemented microscopic tests on Cu(II)-doped paste and ...macro-microscopic tests on S/S Cu(II) contaminated pure clay-particles soil (P-CS), pure silt-particles soil (P-ST), pure sand-particles soil (P-SD), and their mixed soil (CSSM), respectively, with CGF+P all-solid-waste binders (abbreviated as CGF+P binders) composed of calcium carbide residue (CCR), ground granulated blast furnace slag (GGBS), fly ash (FA), and phosphogypsum (PG). The results showed that the clay-minerals in soil determine the S/S efficiency, and Cu(II) threshold content exist in the presence of clay-minerals and absent without clay-minerals. The strength of P-CS and CSSM containing clay-minerals first increased and then decreased with the increase of Cu(II) content, while the leached Cu(Ⅱ) were lower than 2 mg/kg. The strength of P-ST and P-SD without clay-minerals decreased gradually, and the leached Cu(Ⅱ) concentration far higher than 2 mg/kg. Cu(II) ions are immobilized by CGF+P paste and clay-minerals in soil. The S/S mechanism of Cu(II) by CGF+P binders rely on precipitation, adsorption, encapsulation, chemical compound, and ion exchange, and the immobilized mechanism of Cu(II) by clay-minerals through electrostatic attraction, ion exchange, and physical adsorption. However, the binder paste and clay-minerals have the immobilization capacity on Cu(II) ions, is related to the component of the binder and the type of clay-minerals, respectively. The findings provided useful reference for the design and development of solid waste-based binders suitable for S/S heavy metal contaminated soils.
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•The S/S mechanism of Cu(II) was revealed by using microscopic tests of Cu(II)-doped CGF+P all-solid-waste paste.•The S/S mechanism of Cu(II) by CGF+P all-solid-waste binders rely on precipitation, adsorption, encapsulation, chemical compound, and ion exchange.•The efficiency of the CGF+P S/S Cu(II) contaminated soils were better than cement.•The strength and leaching characteristics of CGF+P S/S Cu(II) contaminated P-CS, P-ST), P-SD, and CSSM were revealed, S/S is the coupling of S/S binder and the clay-minerals in soil.•The addition of PG significantly increased the strength of solidified soils but led to a reduction in S/S Cu(II) contaminated soils, which attributed to the retarding effect of Cu(II) and acidic nature of PG.
Mechanochemical treatment with calcium polysulfide (CPS) was applied to remediate the Cr(VI) contaminated soil. The effects of parameters including milling speed, milling time, ball to powder ratio ...(BPR) and dosage of CPS were investigated. The effectiveness of mechanical treatment with or without CPS is estimated by analyzing the leachable fraction of Cr(VI). The results show that mechanochemical treatment with CPS can decrease and immobilize Cr in soil more quickly and efficiently with comparison to the case without additive. Under a milling speed of 500 rpm, milling time of 2 h, BPR of 9 and CPS dosage of 3%, the Cr(VI) leaching concentration significantly decreased from 115 mg L−1 to 0.51 mg L−1, much lower than the regulatory limit of 5 mg L−1. Additionally, XPS results demonstrated that Cr(VI) can be converted into Cr(III) during ball milling with CPS. The high Cr(VI) removal and Cr immobilization capacity makes mechanochemical treatment a great potential in field remediation.
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•Ball milling was carried out to remediating Cr(Ⅵ) contaminated soil with CPS.•Reduction reaction between Cr(Ⅵ) in contaminated soil and CPS happened.•After treatment, leachable Cr(Ⅵ) concentration reduced and be lower than 5 mg L−1.
Mechanochemical techniques have been garnering growing attention in remediation of contaminated soil. This paper summarizes the performance, mechanism, influential factors, and environmental impacts ...of mechanochemical remediation (MCR) for persistent organic pollutants (POPs) contaminated soil and heavy metal(loid) s (HMs) contaminated soil. Firstly, in contrast to other technologies, MCR can achieve desirable treatment of POPs, HMs, and co-contaminated soil, especially with high-concentration pollutants. Secondly, POPs undergo mineralization via interaction with mechanically activated substances, where aromatic and aliphatic pollutants in soil may go through varied degradation routes; inorganic pollutants can be firmly combined with soil particles by fragmentation and agglomeration induced by mechanical power, during which additives may enhance the combination but their contact with anionic metal(loid)s may be partially suppressed. Thirdly, the effect of MCR primarily hinges on types of milling systems, the accumulation of mechanical energy, and the use of reagents, which is basically regulated through operating parameters: rotation speed, ball-to-powder ratio, reagent-to-soil ratio, milling time, and soil treatment capacity; minerals like clay, metal oxides, and sand in soil itself are feasible reagents for remediation, and alien additives play a crucial role in synergist and detoxification; additionally, various physicochemical properties of soil might influence the mechanochemical effect to varying degrees, yet the key influential performance and mechanism remain unclear and require further investigation. Concerning the assessment of soil after treatment, attention needs to be paid to soil properties, toxicity of POPs' intermediates and leaching HMs, and long-term appraisement, particularly with the introduction of aggressive additives into the system. Finally, proposals for current issues and forthcoming advancements in this domain are enumerated in items. This review provides valuable insight into mechanochemical approaches for performing more effective and eco-friendly remediation on contaminated soil.
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•MCR can achieve desirable POPs degradation and HMs immobilization in soil.•MCR mechanisms for POPs degradation and HMs immobilization are proposed.•Soil properties that possibly influence the MCR are elucidated.•Comprehensive assessment should be considered for MCR application.
In this study, the planetary ball milling with CaO addition was used to remediate lindane-contaminated soil. Based on Hertzian theory, a mathematical model was proposed to simulate the trajectory of ...grinding ball and the local energy transfer during a planetary operation at the disk rotation velocities of 150–250 rpm. Besides, the influence of different parameters on lindane removal in soil was investigated, whose results showed that disk rotation velocity and reagent-to-soil ratio had a positive effect, while soil moisture, initial concentration of lindane, and mass of polluted soil demonstrated a negative influence. The mechanochemical method exhibited a higher degradation performance at 3 wt% CaO addition, and a disk rotation velocity of 250 rpm. Active species generated by ball collisions in the presence of CaO, especially superoxide (·O2−) demonstrated a significant role in participating in the lindane conversion. In combination with GCMS and XPS analysis, the proposed model provides insight into mechanochemical remediation process from physical and chemical perspectives, which mainly includes four main steps: mixing, inducing, chemical reaction, and structure destruction.
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•Efficient degradation of lindane by CaO-mechanochemical method broadens numerical model application.•The efficiency accumulation energy (D0) related to CR and Pe0 was adopted to investigate the local energy transfer.•Superoxide (·O2−) played a crucial role on the mechanochemical degradation.
Chemical stabilization is frequently used to stabilize lead (Pb) or arsenate (As), but faces challenges in Pb-As co-contaminated soils because of the antagonistic reactions between chemical ...stabilizers and contaminants. In this work, we innovated an effective and cost-efficient stepwise steam flash heating (SSFH) strategy to simultaneously immobilize Pb and As, and unraveled the underlying mechanisms. The combination of 1.5% Ca(H2PO4)2 and 2% Fe2(SO4)3 only decreased 1.99% Pb by toxicity characteristic leaching procedure (TCLP-Pb) but increased 17.8% of TCLP-As due to the antagonistic effects. SSFH with Ca(H2PO4)2 in the first step and Fe2(SO4)3 in the second step achieved the minimal TCLP-Pb and TCLP-As of 0.778 and 0.327 mg/L, respectively. It also reduced 69.8% of leachable As in 100-year acid rain simulation, indicating a favorable long-term stabilization performance. Additionally, SSFH approach reduced 43.2% stabilizer dosage and 14.9% cost. X-ray absorption near edge structure (XANES) documented that the stepwise SFH promoted the transformation of Pb(NO3)2 and NaAsO2/NaAsO3/As2O3/As2O5 into stable Pb3(PO4)2 and FeAsO4, preventing the formation of AsO43- and FePO4. Our findings proved the state-of-the-art SSFH approach and unraveled its mechanisms to stabilize Pb and As co-contamination in soils, offering a green and sustainable remediation alternative for the management of heavy metal contaminated sites.
A novel stepwise SFH approach can be applied to overcome the stabilizer antagonist effects by separately immobilizing Pb and As in two sequential steps. It also decreased 43.2% of stabilizer dosage and 14.9% of cost comparing to conventional chemical stabilization. This approach can be used for other metal co-contaminated soils facing similar antagonistic challenges, and our work raises a state-of-the-art solution for cost-effective, green and sustainable remediation practices.
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•Innovative stepwise steam flash heating (SSFH) for effective Pb and As immobilization.•SSFH efficiently eliminated the antagonistic effect by stabilizers.•Higher cost-efficiency and favorable long-term immobilization performance in SSFH.•SSFH changes Pb and As immobility mechanism evidenced by XANES.
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•Direct oxidation of TPHs was achieved by complex Fe/Mn-SOM in situ.•Fe/Mn bound to SOM was formed by –COOH, O-H, and C-O-C.•Direct oxidation of TPHs by ROSs was the primary ...pathway.•Fe/Mn-SOM-PS* complex formed in-situ accelerated PS activation.
Although the activation of persulfate (PS) by exogenous activators for the removal of adsorbed total petroleum hydrocarbons (TPHs) in soil has been widely reported, the ineffective consumption of the reactive oxygen species (ROSs) during the process of diffusion to the surface of soil particles has received little attention. In this study, a novel Fe/Mn oxide cross-linked with soil organic matter (Fe/Mn-SOM complex) was successfully preformed in situ. Characterization analysis revealed the dominant components of Fe/Mn-SOM complex were mainly FeOOH and MnO2, which bound to SOM through –COOH, O-H, and C-O-C interactions. In Fe/Mn-SOM/PS system, the removal efficiencies reached 75.74 % for TPHs (23042 mg/kg), 71.02 % for alkanes (13646 mg/kg), and 80.60 % for polycyclic aromatic hydrocarbons (PAHs, 4712 mg/kg), representing an increase of 19.98 ∼ 32.29 % compared to the (Fe2++ Mn2+)/PS system. Furthermore, the Fe/Mn-SOM complex exhibited resistance to common organic matter in the soil, such as humic acids, urea, and lignin. Radical capture and quenching experiments indicated that sulfate radicals (SO4•-), hydroxyl radicals (•OH), and superoxide radicals (O2•-) played key roles in TPHs removal in the Fe/Mn-SOM system. It can be inferred that Fe/Mn-SOM-PS* formed through electron transfer accelerated the activation of PS, with SO4•- and •OH generated on the surface of the Fe/Mn-SOM complex directly oxidizing nearby petroleum hydrocarbons through ternary complexes (TPHs-Fe/Mn-SOM complex). O2•- also contributed to the reduction of Fe and Mn active species, facilitating PS activation for TPHs removal. Furthermore, potential degradation pathways of TPHs were proposed using GC–MS in conjunction with density functional theory (DFT) calculations. This study offers a fresh perspective on the chemical remediation of petroleum-contaminated soil.
