Stabilization and solidification of Pb in cement matrices

Simultaneous Immobilization of Heavy Metals in MKPC-Based Mortar-Experimental Assessment

Heavy metal contamination, associated with the increase in industrial production and the development of the population in general, poses a significant risk in terms of the contamination of soil, water, and, consequently, industrial plants and human health. The presence of ecotoxic heavy metals (HMs) thus significantly limits the sustainable development of society and contributes to the deterioration of the quality of the environment as a whole. For this reason, the stabilization and immobilization of heavy metals is a very topical issue. This paper deals with the possibility of the simultaneous immobilization of heavy metals (Ba2+, Pb2+, and Zn2+) in mortar based on magnesium potassium phosphate cement (MKPC). The structural, mechanical, and hygric parameters of mortars artificially contaminated with heavy metals in the form of salt solutions were investigated together with the formed hydration products. In the leachates of the prepared samples, the content of HMs was measured and the immobilization ratio of each HM was determined. The immobilization rate of all the investigated HMs was >98.7%, which gave information about the effectiveness of the MKPC-based matrix for HM stabilization. Furthermore, the content of HMs in the leachates was below the prescribed limits for non-hazardous waste that can be safely treated without any environmental risks. Although the presence of heavy metals led to a reduction in the strength of the prepared mortar (46.5% and 57.3% in compressive and flexural strength, respectively), its mechanical resistance remained high enough for many construction applications. Moreover, the low values of the parameters characterizing the water transport (water absorption coefficient Aw = 4.26 × 10-3 kg·m-2·s-1/2 and sorptivity S = 4.0 × 10-6 m·s-1/2) clearly demonstrate the limited possibility of the leaching of heavy metals from the MKPC matrix structure.

Ternary Blends for Self-Compacting Mortars Production Composed by Electric Arc Furnace Dust and Other Industrial by-Products

This study is framed within the circular economy model through the valorisation of industrial by-products. This research shows the results of producing self-compacting mortars (SCMs) with electric arc furnace dust (EAFD) and other industrial by-products such as fly ash, conforming (FA) or not conforming (NcFA), from coal-fired power plants, or recovery filler (RF) from hot-mix asphalt plants. Three batches of SCMs, each with one industrial-by product (FA, NcFA, or RF), and three levels of EAFD ratio incorporation (0%, 10%, 20%), were tested. An extra batch with a greater amount of FA was manufactured. When the incorporation ratio of EAFD rose, the mechanical strength decreased, due to the presence of a calcium zinc hydroxide dihydrate phase; nevertheless, this decrease diminished over time. All SCM mixes, except the 40C 40FA 20 EAFD mix, were above 20 MPa at 28 days. All mixes named 70C and 40C reached 40 and 30 MPa, respectively, at 90 days. Mixes with EAFD showed less capillarity and no difference in water absorption by immersion with respect to mixes without EAFD after 91 days. The SCMs designed proved to be stable in terms of leaching of the heavy metals contained in EAFD, where all the hardened SCMs were classified as inert.

Sewage sludge ash-incorporated stabilisation/solidification for recycling and remediation of marine sediments

Finding suitable disposal sites for dredged marine sediments and incinerated sewage sludge ash (ISSA) is a challenge. Stabilisation/solidification (S/S) has become an increasingly popular remediation technology. This study sheds light on the possible beneficial use of ISSA together with traditional binders to stabilise/solidify marine sediments. The performance of the binders on S/S of sediment 1 (clean) and sediment 2 (contaminated) was also compared. The results showed that the use of ISSA as part of the binder was effective in promoting the strength of the sediment with a high initial moisture content due to ISSA porous and high water absorption characteristics. The sediments treated with 10% cement and 20% ISSA attained the highest strength. Also, cement hydration as well as pozzolanic reactions between ISSA and Ca(OH)₂ made contributions to the strength development. This was supported by the microstructural analysis, in particular the porosity results. In terms of environmental impacts, two leaching tests (toxicity characteristic leaching procedure and synthetic precipitation leaching procedure) found that all the S/S treated sediment by 10% lime and 20% ISSA resulted in the lowest leachate concentrations under the on-site reuse scenario or under simulative acidic rainfall conditions. Therefore, recycling waste ISSA with lime can be used as an appealing binder to replace cement to stabilise/solidify dredged marine sediments for producing fill materials.

Cement-stabilized contaminated soil: Understanding Pb retention with XANES and Raman spectroscopy

Cement-based stabilization is a widespread technique used for the treatment of contaminated soils. Despite its established application, the mechanisms involved in the stabilization of contaminants are not fully understood yet. This work aims to elucidate the fate of a real Pb contaminated soil amended with different binders, by studying Pb local environment prior and after the stabilization process. The study of a complex historically contaminated soil was coupled with the investigation of simplified artificial systems, developed to model Pb local structure in the unknown newly formed hybrid systems of soil and binders. The use of synchrotron-based element-specific X-ray absorption spectroscopy (XAS) permitted to probe the actual transformation of Pb environment in the real contaminated soil after the stabilization process. With the support of the model systems, we can propose as the main mechanism involved in Pb retention in sulfated soil treated with cement, the incorporation and/or adsorption of Pb on calcium silicate hydrates and ettringite.

Detoxification and immobilization of chromite ore processing residue using the alkali-activated cementitious materials mixed with ascorbic acid

The existence of leachable Cr(Ⅵ) in chromite ore processing residue (COPR) makes it hazardous waste. Therefore, resourceful utilization of COPR is necessary to protect the ecosystem and living biota from hazardous effect of Cr(Ⅵ) caused by its leaching. In this study, detoxification and immobilization of COPR was carried out through introduction of ascorbic acid (AA) in alkali-activated cementitious materials. Several dosages of AA were treated with water extractable/soluble Cr(Ⅵ) to achieve the optimum dosage which could be further utilized in solidification process. While, the compressive strength was developed through utilizing different modulus of water glass, liquid to solid ratios and curing temperatures. The results showed that 0.3% of AA was enough to reduce the Cr(Ⅵ) into Cr(Ⅲ), and highest compressive strength of 120 MPa was achieved after using the modulus of 1.6, liquid to solid ratio of 0.24 and curing temperature of 30 °C. The solidified samples having AA had not exceeded the toxicity limit up to 60% addition of COPR, and samples without addition of AA were effective for solidification of 20% COPR. Regarding mechanism, the compressive strength, leaching behavior and microscopic analysis i.e. X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR) and scanning electron microscope with energy dispersive spectrometry (SEM-EDS) showed that immobilization of chromium was carried out through physical and chemical means.

Effects of Long-Term Repeated Freeze-Thaw Cycles on the Engineering Properties of Compound Solidified/Stabilized Pb-Contaminated Soil: Deterioration Characteristics and Mechanisms

The effects of long-term repeated freeze-thaw cycles and pollution levels on the engineering properties (q_u, E₅₀, φ, c, and k) of Pb-contaminated soils were investigated in various laboratory tests. These soils were solidified/stabilized (S/S) with three types of cement-based combined binders (C2.5S5F5, C5S2.5F2.5, and C5S5, cement, lime, and fly ash, mixed in different proportions; these materials are widely used in S/S technology). The strength and permeability coefficient of compound solidified/stabilized Pb-contaminated soils (Pb-CSCSs) were determined based on measurements of unconfined compressive strength (UCS), direct shear, and permeability. CT scanning, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) tests were employed to analyse the deterioration mechanisms under various repetitions of freeze-thaw cycles. The results showed that, under repeated freeze-thaw cycles, the engineering properties of Pb-CSCSs all degraded to varying degrees, though degradation tended to stabilise after 30 days of freeze-thaw cycles. The study also found that the pollutants obstruct hydration and other favourable reactions within the soil structure (such as ion exchanges and agglomerations and pozzolanic reactions). The activation of hydration reactions and the rearrangement of soil particles by freeze-thaw cycles thus caused the engineering properties to fluctuate, and soils exhibited different deterioration characteristics with changes in Pb²⁺ content.

Recycling hazardous textile effluent sludge in cement-based construction materials: Physicochemical interactions between sludge and cement

The textile industry produces a large amount of textile effluent sludge (TES). Many studies have explored the potential use of TES in cement-based materials. However, the physicochemical interactions between the TES and ordinary Portland cement (OPC) have rarely been studied. In this study, the effects of increasing dosage (0-20% by OPC) of TES on the performance of OPC-TES blends were investigated in terms of hydration progress, mechanical strength, microstructure evolution and metal leachability. The results showed that TES markedly delayed the OPC hydration at the early age, and increasing dosages of TES decreased the portlandite content at 7 and 28 days' age. Compared to the reference, the OPC-TES mortar exhibited seriously degraded mechanical strength; when using 20% TES, the decrease in compressive and flexural strength reached up to 71% and 42% respectively at the age of 28 days. Scanning electron microcopy and mercury intrusion porosimetry found the inclusion of TES introduced more weak interfaces in the cement mortar, thus increased the total porosity especially the macropores. But leachability tests revealed all the toxic metals in the TES were stabilized after the incorporation of OPC and exhibited very low metal mobility in the OPC-TES mortar, which posed no environmental risk.

Hydration of Ordinary Portland Cement in Presence of Lead Sorbed on Ceramic Sorbent

Lead, a highly toxic element, is frequently present in various solid wastes as well as in industrial effluents. Sorption with a low cost sorbent is a simple way of Pb removal from liquid streams, but stabilization of spent sorbent has to be ensured in order to prevent Pb leaching out and possible environmental contamination. In previous research, ceramic sorbent, generated as waste product in brick industry, was tested as sorbent and proved high sorption capacity for lead. Lead was sorbed partially as hydrocerussite and partially as adsorbed surface layer. The Pb leaching from sorbent was very high and thus further immobilization of sorbent was necessary. Lead, as well as other heavy metals, is known as retarder of the hydration process of Ordinary Portland Cement (OPC), used for the immobilization. In this paper, influence of sorbed Pb and PbO, as reference compound, on cement hydration was studied by calorimetry, thermogravimetry and Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy (MAS NMR). The sorbed lead was found to be less detrimental to hydration retardation due to the lower solubility of precipitated hydrocerussite in basic environment compared to PbO, which forms plumbate anion.

Innovative solidification/stabilization of lead contaminated soil using incineration sewage sludge ash

The proper treatment of lead (Pb) contaminated soils and incinerated sewage sludge ash (ISSA) has become an environmental concern. In this study, ordinary Portland cement (OPC) and blended OPC containing incinerated sewage sludge ash (ISSA) were used to solidify/stabilize (S/S) soils contaminated with different concentrations of Pb. After curing for 7 and 28 d, the S/S soils were subjected to a series of strength, leaching and microscopic tests. The results showed that replacement of OPC by ISSA significantly reduced the unconfined compressive strength (UCS) of S/S soils and leached Pb. In addition, the leaching of Pb from the monolithic samples was diffusion controlled, and increasing the ISSA addition in the samples led to a lower diffusion coefficient and thus an increase in the feasibility for "controlled utilization" of S/S soils. Furthermore, the proposed S/S method significantly decreased the amount of Pb associated with carbonates and increased the amount of organic and residual Pb in S/S soils, reflecting that the risk of Pb contaminated soils can be effectively mitigated by the incorporating of ISSA. Overall, the leachability of Pb was controlled by the combined effect of adsorption, encapsulation or precipitation in the S/S soils.

Management practices for end-of-life cathode ray tube glass: Review of advances in recycling and best available technologies

Cathode ray tubes are image display units found in computer monitors and televisions. In recent years, cathode ray tubes have been generated as waste owing to the introduction of newer and advanced technologies in image displays, such as liquid crystal displays and high definition televisions, among others. Generation and subsequent disposal of end-of-life cathode ray tubes presents a challenge owing to increasing volumes and high lead content embedded in the funnel and neck sections of the glass. Disposal in landfills and open dumping are anti-environmental practices considering the large-scale contamination of environmental media by the potential of toxic metals leaching from glass. Mitigating such environmental contamination will require sound management strategies that are environmentally friendly and economically feasible. This review covers existing and emerging management practices for end-of-life cathode ray tubes. An in-depth analysis of available technologies (glass smelting, detoxification of cathode ray tube glass, lead extraction from cathode ray tube glass) revealed that most of the techniques are environmentally friendly, but are largely confined to either laboratory scale, or are often limited owing to high cost to mount, or generate secondary pollutants, while a closed-looped method is antiquated. However, recycling in cementitious systems (cement mortar and concrete) gives an added advantage in terms of quantity of recyclable cathode ray tube glass at a given time, with minimal environmental and economic implications. With significant quantity of waste cathode ray tube glass being generated globally, cementitious systems could be economically and environmentally acceptable as a sound management practice for cathode ray tube glass, where other technologies may not be applicable.

Solidification/stabilization and leaching behavior of PbCl₂ in fly-ash hydrated silicate matrix and fly-ash geopolymer matrix

Fly ash (FA) for reuse as a construction material is activated using two methods, to produce hydrated silicate and geopolymer gels. We investigated the solidification/stabilization and leaching behavior of PbCl2 in a geopolymer matrix (GM) and hydrated silicate matrix (HSM), based on FA as the source material, to evaluate the environmental and health risks. The GM and HSM synthetic conditions were 60 °C, 20 % relative humidity (RH), and 12 wt% (6 mol/L) NaOH, and 20 ± 2 °C, ≥ 90 % RH, and 30 wt.%, respectively, based on their compressive strength performances. X-ray diffraction (XRD) showed that Pb participated in hydration and geopolymerization, and was incorporated in the structural components of the hydrated silicate and geopolymer. In leaching experiments, the solidification/stabilization effects of Pb and Cl in the HSM and GM improved with increasing curing time. After long-term curing (28 days), the immobility of Pb in the GM was better than that in the HSM. Sodalite improved the Cl-stabilizing ability of the GM compared with that of the HSM. In static monolithic leaching experiments, HSM and GM had the same Pb-leaching behaviors. Based on the changes in the location of the neutral sphere layer with decreasing acid-neutralizing capacity, Pb release was divided into alkaline-release, stagnation, and acid-release stages. The neutral sphere layer contained the highest Pb concentration during permeation toward the block center from the block edge. This behavior regulation could also apply to other amphoteric metals immobilized by GMs and HSMs.

Green remediation and recycling of contaminated sediment by waste-incorporated stabilization/solidification

Navigational/environmental dredging of contaminated sediment conventionally requires contained marine disposal and continuous monitoring. This study proposed a green remediation approach to treat and recycle the contaminated sediment by means of stabilization/solidification enhanced by the addition of selected solid wastes. With an increasing amount of contaminated sediment (20-70%), the 28-d compressive strength of sediment blocks decreased from greater than 10MPa to slightly above 1MPa. For augmenting the cement hydration, coal fly ash was more effective than lime and ground seashells, especially at low sediment content. The microscopic and spectroscopic analyses showed varying amounts of hydration products (primarily calcium hydroxide and calcium silicate hydrate) in the presence of coal fly ash, signifying the influence of pozzolanic reaction. To facilitate the waste utilization, cullet from beverage glass bottles and bottom ashes from coal combustion and waste incineration were found suitable to substitute coarse aggregate at 33% replacement ratio, beyond which the compressive strength decreased accordingly. The mercury intrusion porosimetry analysis indicated that the increase in the total pore area and average pore diameter were linearly correlated with the decrease of compressive strength due to waste replacement. All the sediment blocks complied with the acceptance criteria for reuse in terms of metal leachability. These results suggest that, with an appropriate mixture design, contaminated sediment and waste materials are useful resources for producing non-load-bearing masonry units or fill materials for construction uses.

Treatment of toxic metal aqueous solutions: encapsulation in a phosphate-calcium aluminate matrix

Polyphosphate-modified calcium aluminate cement matrices were prepared by using aqueous solutions polluted with toxic metals as mixing water to obtain waste-containing solid blocks with improved management and disposal. Synthetically contaminated waters containing either Pb or Cu or Zn were incorporated into phosphoaluminate cement mortars and the effects of the metal's presence on setting time and mechanical performance were assessed. Sorption and leaching tests were also executed and both retention and release patterns were investigated. For all three metals, high uptake capacities as well as percentages of retention larger than 99.9% were measured. Both Pb and Cu were seen to be largely compatible with this cementitious matrix, rendering the obtained blocks suitable for landfilling or for building purposes. However, Zn spoilt the compressive strength values because of its reaction with hydrogen phosphate anions, hindering the development of the binding matrix.

Solidification/stabilization of toxic metals in calcium aluminate cement matrices

The ability of calcium aluminate cement (CAC) to encapsulate toxic metals (Pb, Zn and Cu) was assessed under two curing conditions. Changes in the consistency and in the setting time were found upon the addition of the nitrates of the target metals. Both Pb and Cu caused a delay in CAC hydration, while Zn accelerated the stiffening of the mortar. Compressive strengths of the metal-doped mortars, when initially cured at 60 °C/100% RH, were comparable with that of the free-metal mortar. Three different pore size distribution patterns were identified and related to the compounds identified by XRD and SEM. Sorbent capacities of CAC for the toxic metals were excellent: a total uptake was achieved for up to 3 wt.% loading of the three metals. In this way, CAC mortars were perfectly able to encapsulate the toxic metals, allowing the use of CAC for waste management as proved by the leaching tests.

Immobilization of Lead from Pb-Contaminated Soil Amended with Peat Moss

Immobilization of lead (Pb) using soil amendments can reduce Pb toxicity and bioavailability in soil. This study evaluated Pb immobilization in a Pb-contaminated soil by using peat moss through various tests. The Pb-contaminated soil (2000 mg Pb·kg−1) was amended with 1%, 5%, and 10% of peat moss to immobilize Pb in the soil. The immobilization properties of Pb in the contaminated soil were evaluated by a column leaching experiment, a microcosm test, and a batch incubation test. Peat moss significantly reduced the Pb leaching in all of the experiments and more effectively reduced mobility and toxicity of Pb in the column leaching and microcosm tests than bioavailability in the batch incubation test. The immobilized lead from the soils amended with 1%, 5%, and 10% of peat moss was 37.9%, 87.1%, and 95.4% from the column leaching test, 18.5%, 90.9%, and 96.4% from the microcosm test, and 2.0%, 36.9%, and 57.9% from the NH4NO3extraction method, respectively, indicating that peat moss can be effectively used for the remediation of Pb-contaminated soil.

Influence of leaching conditions on the release kinetics of lead, chromium and nickel from solidified/stabilized cementitious materials

In this work, we investigate, on a laboratory scale, the influence of the leaching conditions on the release of various chemical elements from a cementitious material obtained by solidification of PbO, Ni2O3 and Cr2O3 with blended cement (CEMII-B32.5, according to European Standards). The pH effects on the pollutants release and the composition of the initial pore solution (target elements: chloride, sulfate, sodium, potassium, calcium, lead, chromium and nickel) were assessed through an experimental procedure consisting of two equilibrium leaching tests [the acid neutralization capacity (ANC) and the pore water (PW) tests] and the maximum mobile fraction (MMF) text. Samples of the same material were submitted in parallel to dynamic leaching tests in order to assess the influence of the boundary conditions (instantaneous liquid/solid (L/S) ratio, solution renewal) on the leaching kinetics of the target elements. The comparison criteria were the leachate saturation state, the released cumulative quantities and the leaching flux. Generally, leachate quantities obtained by the ANC, PW and MMF tests were important. However, the lowest released amount was observed for the monolith leaching test, and leachate saturation slowed down the dynamic release. Finally, experimental results highlighted another important parameter: the influence of the liquid/solid contact type on leaching kinetics.

Encapsulation, solid-phases identification and leaching of toxic metals in cement systems modified by natural biodegradable polymers

Cement mortars loaded with Cr, Pb and Zn were modified by polymeric admixtures [chitosans with low (LMWCH), medium (MMWCH) and high (HMWCH) molecular weight and hydroxypropylchitosan (HPCH)]. The influence of the simultaneous presence of the heavy metal and the polymeric additive on the fresh properties (consistency, water retention and setting time) and on the compressive strength of the mortars was assessed. Leaching patterns as well as properties of the cement mortars were related to the heavy metals-bearing solid phases. Chitosan admixtures lessened the effect of the addition of Cr and Pb on the setting time. In all instances, chitosans improved the compressive strength of the Zn-bearing mortars yielding values as high as 15 N mm(-2). A newly reported Zn phase, dietrichite (ZnAl(2)(SO(4))(4)·22H(2)O) was identified under the presence of LMWCH: it was responsible for an improvement by 24% in Zn retention. Lead-bearing silicates, such as plumalsite (Pb(4)Al(2)(SiO(3))(7)), were also identified by XRD confirming that Pb was mainly retained as a part of the silicate network after Ca ion exchange. Also, the presence of polymer induced the appearance and stabilization of some Pb(IV) species. Finally, diverse chromate species were identified and related to the larger leaching values of Cr(VI).

Experimental investigation of influence of acid rain on leaching and hydraulic characteristics of cement-based solidified/stabilized lead contaminated clay

Remediation of contaminated lands in China urban areas is of great concern. Degradation of construction facilities caused by acid rain is a serious environmental pollution issue in China. This paper presents an investigation of the effects of acid rain on leaching and hydraulic properties of cement-based solidified/stabilized lead contaminated soil. Laboratory tests including infiltration test and soaking test are conducted. It is found that the soil hydraulic conductivity decreases with increase in the pore volume of flow of permeant liquids (acid rain and distilled water). The decreasing rate in the case of the acid rain is lower than that in the case of the distilled water. The soaking test results show that pH and the presence of sulfate ions of acid rain have considerable influence on the leached concentrations and leaching rate of calcium.

Interaction of carboxymethylchitosan and heavy metals in cement media

The performance of an etherified chitosan, carboxymethylchitosan (CMCH), when added to cement mortars doped with heavy metals, was assessed. In the presence of heavy metals (Cr, Pb, Zn) strong modifications of the fresh-state properties were evaluated. The addition of the polymer was seen to be useful in minimising some of these modifications, as those related to the setting time. A competitive mechanism for adsorption between the oxoanionic form of the metals and the carboxylate groups of the chitosan derivative was established. Studies on the metal chelating ability of the polymer and leaching from the hardened specimens showed scarce complexation under alkaline conditions, pointing to physical entrapment based on metal adsorption. However, significant chelation of metals was proved at near-neutral pH, suggesting the potential usefulness of the polymer as an agent for removing heavy metals from polluted waters and subsequently immobilizing them in cement mortars. Leaching tests carried out on polymer-metal complex-bearing samples showed a reduction in the amount of released Pb and Zn.

Efficiency modeling of solidification/stabilization of multi-metal contaminated industrial soil using cement and additives

In a laboratory study, formulations of 15% (w/w) of ordinary Portland cement (OPC), calcium aluminate cement (CAC) and pozzolanic cement (PC) and additives: plasticizers cementol delta ekstra (PCDE) and cementol antikorodin (PCA), polypropylene fibers (PPF), polyoxyethylene-sorbitan monooleate (Tween 80) and aqueous acrylic polymer dispersion (Akrimal) were used for solidification/stabilization (S/S) of soils from an industrial brownfield contaminated with up to 157, 32,175, 44,074, 7614, 253 and 7085mg kg(-1) of Cd, Pb, Zn, Cu, Ni and As, respectively. Soils formed solid monoliths with all cementitious formulations tested, with a maximum mechanical strength of 12N mm(-2) achieved after S/S with CAC+PCA. To assess the S/S efficiency of the used formulations for multi-element contaminated soils, we propose an empirical model in which data on equilibrium leaching of toxic elements into deionized water and TCLP (toxicity characteristic leaching procedure) solution and the mass transfer of elements from soil monoliths were weighed against the relative potential hazard of the particular toxic element. Based on the model calculation, the most efficient S/S formulation was CAC+Akrimal, which reduced soil leachability of Cd, Pb, Zn, Cu, Ni and As into deionized water below the limit of quantification and into TCLP solution by up to 55, 185, 8750, 214, 4.7 and 1.2-times, respectively; and the mass transfer of elements from soil monoliths by up to 740, 746, 104,000, 4.7, 343 and 181-times, respectively.