Study on use of MSWI fly ash in ceramic tile

In this work, MSWI (municipal solid waste incineration) fly ash is used as a blending in production of ceramic tile by taking advantage of its high contents of SiO(2), Al(2)O(3) and CaO. Besides, macro-performance and microstructure of the product as well as its leaching toxicity in practical application were studied by means of XRD, IR and SEM analysis, and leaching toxicity and sequential chemical extraction analysis of the product. It is found that when 20% fly ash is added, the product registers a high compressive strength of 18.6MPa/cm(2) and a low water absorption of 7.4% after being sintered at 960 degrees C. It is found that the glazed tile shows excellent resistance against leaching, in accordance with HVEP stand, of heavy metals with Cd<0.0002ppm, Pb<0.0113ppm and Zn<0.0749ppm, and Hg below the low detection limit. These results show that heavy metals are cemented among the solid lattice in the product and can hardly be extracted. Leaching toxicity of heavy metals in the product, especially Hg, Pb, Zn and Cd, is substantially reduced to less than one-tenth of that in fly ash. In addition, specifications of Hg, Pb, Zn and Cd are largely changed and only a small portion of these heavy metals exists in soluble phases. These results as a whole suggest that the use of MSWI fly ash in ceramic tile constitutes a potential means of adding value.     

Efficiency of a zeolitized pumice waste as a low-cost heavy metals adsorbent

The unextracted residue obtained after a countercurrent two-step extractive process of silica from pumice lapillus, at 100 degrees C and room pressure, has been found mainly crystallized to the pseudo-cubic form typical of zeolite P. This residue could be active as a low-cost agent for the removal of heavy metals from wastewater. In this paper the removal capacity of six metallic cations (i.e. Cu(2+), Ni(2+), Zn(2+), Cd(2+), Pb(2+) and Cr(3+)) was studied in a stirred batch reactor. Results obtained showed that the removal of metal ions (100-500mgg(-1)) from wastewater is achieved in a short time and the concentration lowered under the legal limits. The adsorption mechanism mainly involves an ionic exchange between sodium ions from the solid phase and heavy metals in solution. However, if wastewater was accompanied by free acidity, it first should be neutralized to pH 4-5 to prevent zeolite destruction.     

Vitrification of fly ash from municipal solid waste incinerator

Fly ash from municipal solid wastes (MSW) incinerators in Korea contains a large amount of toxic materials and requires pertinent treatments. However, since fly ash in Korea has a high chlorine concentration, it is difficult to apply cementation and chemical treatment techniques. In this study, we report the vitrification of fly ash along with the properties of the glasses and leaching characteristics of heavy metal ions.Fly ash can be vitrified by melting at 1500 degrees C for 30 min with the addition of >5 wt.% of SiO2. Glasses showed Vickers hardness of 4000-5000 MPa, bending strength of 60-90 MPa and indentation fracture toughness of approximately 0.9 MPa m(1/2). Glasses also showed the excellent resistance against leaching of heavy metal ions with Cd2+ <0.04 ppm, Cr3+ <0.02 ppm, Cu2+ <0.04 ppm and Pb2+ <0.2 ppm. These results indicate that the vitrification technique is effective for the stabilization and recycling of toxic incinerator fly ash.     

Competitive sorption and transport of Pb2+, Ni2+, Mn2+, and Zn2+ in lateritic soil columns

Knowledge of sorption and transport of heavy metals in soils in the presence of other metals is crucial for assessing the environmental risk of these metals. Competitive sorption and transport of four metals, Pb(2+), Ni(2+), Zn(2+), and Mn(2+), were investigated using multi-metal column experiments with lateritic soils obtained from a gold mine impacted by acid mine drainage. Based on Pb(2+) breakthrough time for single-metal system at a pH of approximately 5, the sorption capacity of Pb(2+) was estimated to be higher in lateritic soil than the other metals. For multi-metal systems, the estimated retardation factors for the metals from highest to lowest were: Pb(2+)>Zn(2+)～ Ni(2+)>Mn(2+), suggesting the mobility of metals through lateritic soil for a multi-metal system would be in the order of Mn(2+)>Ni(2+)～ Zn(2+)>Pb(2+). For binary and multi-metal systems, the estimated sorption capacities of individual metals were found to be lower than the sorption capacities in single metal system - indicating possible competition for sorption sites. Mass recoveries estimates showed that the sorption of metals was more reversible under competitive multi-metal systems than in single metal systems.     

Heavy metals binding properties of esterified lemon

Sorption of Cd(2+), Cr(3+), Cu(2+), Ni(2+), Pb(2+) and Zn(2+) onto a carboxyl groups-rich material prepared from lemon was investigated in batch systems. The results revealed that the sorption is highly pH dependent. Sorption kinetic data indicated that the equilibrium was achieved in the range of 30-240 min for different metal ions and sorption kinetics followed the pseudo-second-order model for all metals studied. Relative sorption rate of various metal cations was found to be in the general order of Ni(2+)>Cd(2+)>Cu(2+)>Pb(2+)>Zn(2+)>Cr(3+). The binding characteristics of the sorbent for heavy metal ions were analyzed under various conditions and isotherm data was accurately fitted to the Langmuir equation. The metal binding capacity order calculated from Langmuir isotherm was Pb(2+)>Cu(2+)>Ni(2+)>Cd(2+)>Zn(2+)>Cr(3+). The mean free energy of metal sorption process calculated from Dubinin-Radushkevich parameter and the Polanyi potential was found to be in the range of 8-11 kJ mol(-1) for the metals studied showing that the main mechanism governing the sorption process seems to be ion exchange. The basic thermodynamic parameters of metals ion sorption process were calculated by using the Langmuir constants obtained from equilibration study. The DeltaG degrees and DeltaH degrees values for metals ion sorption on the lemon sorbent showed the process to be spontaneous and exothermic in nature. Relatively low DeltaH degrees values revealed that physical adsorption significantly contributed to the mechanism.     

Effect of water-extraction on characteristics of melting and solidification of fly ash from municipal solid waste incinerator

This study was conducted to investigate the effect of water-extraction process on the removal of major elements and heavy metals in the fly ash from Municipal Solid Waste Incinerator (MSWI), and their thermal stability in the following melting process. The water-extraction was first applied to extract soluble elements and heavy metals from the fly ash from MSWI at different liquid-to-solid rates (L/S) of 2, 5, and 10, respectively. The extracted fly ash and the raw fly ash were then melted at the temperatures of 1000-1350 degrees C in an electrically heated furnace. The results showed that the compounds of Ca, Na, K, and Cl achieved high removal rates of 30.7-72.8% at L/S=10, respectively, Cr was the most extractable heavy metal with removal rate of 12.3% among the several heavy metals tested. The water-extracted fly ash had better stability as compared to raw one, which was indicated by lower weight loss and better immobilization ability of heavy metals such as Zn, Cu, and Pb in the melting process. The results showed that combing water-extraction and melting process could provide one of the alternatives for treating MSWI fly ash in China for reutilization.     

Ion-exchange of Pb2+, Cu2+, Zn2+, Cd2+, and Ni2+ ions from aqueous solution by Lewatit CNP 80

Removal of trace amounts of heavy metals can be achieved by means of selective ion-exchange processes. The newly developed resins offered a high resin capacity and faster sorption kinetics for the metal ions such as Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) ions. In the present study, the removal of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) ions from aqueous solutions was investigated. Experimental investigations were undertaken using the ion-exchange resin Lewatit CNP 80 (weakly acidic) and were compared with Lewatit TP 207 (weakly acidic and chelating). The optimum pH range for the ion-exchange of the above mentioned metal ions on Lewatit CNP 80 and Lewatit TP 207 were 7.0-9.0 and 4.5-5.5, respectively. The influence of pH, contact time, metal concentration and amount of ion-exchanger on the removal process was investigated. For investigations of the exchange equilibrium, different amounts of resin were contacted with a fixed volume of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) ion containing solution. The obtained sorption affinity sequence in the presented work was Ni(2+)>Cu(2+)>Cd(2+)>Zn(2+)>Pb(2+). The metal ion concentrations were measured by AAS methods. The distribution coefficient values for metal ions of 10(-3)M initial concentration at 0.1mol/L ionic strength show that the Lewatit CNP 80 was more selective for Ni(2+), Cu(2+) than it was for Cd(2+), Zn(2+) and Pb(2+). Langmuir isotherm was applicable to the ion-exchange process and its contents were calculated. The uptake of metal ions by the ion-exchange resins was reversible and thus has good potential for the removal of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) from aqueous solutions. The amount of sorbed metal ion per gram dry were calculated as 4.1, 4.6, 4.7, 4.8, and 4.7mequiv./g dry resin for Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+), respectively. Selectivity increased in the series: Cd(2+)>Pb(2+)>Cu(2+)>Ni(2+)>Zn(2+). The results obtained showed that Lewatit CNP 80 weakly acidic resin had shown better performance than Lewatit TP 207 resin for the removal of metals. The change of the ionic strength of the solution exerts a slight influence on the removal of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+). The presence of low ionic strength or low concentration of NaNO(3) does not have a significant effect on the ion-exchange of these metals by the resins. We conclude that Lewatit CNP 80 can be used for the efficient removal of Pb(2+), Cu(2+), Zn(2+), Cd(2+), and Ni(2+) from aqueous solutions.     

Thermal treatment of the fly ash from municipal solid waste incinerator with rotary kiln

Reuse of the fly ash from the municipal solid waste incinerator (MSWI) is a policy of Taiwan EPA. However, the fly ash is often classified as a hazardous waste and cannot be reused directly because the concentrations of heavy metals exceed the TCLP regulations. The main objective of this study is to investigate the continuous sintering behavior of fly ash with a rotary kiln and seek a solution to reduce the concentrations of heavy metal to an acceptable value. The partitions of the heavy metals in the process are also considered. The results of TCLP showed that among the metals of Cr, Cd, Cu and Pb, only the concentrations of Pb in raw fly ash exceeded the regulation. At sintering temperatures of 700, 800 and 900 degrees C, the concentration of Pb decreased in sintering products, however, the concentration of Pb still exceeded the limitation at 700 and 800 degrees C. Additionally, the water-washing was used to pre-treat the fly ash before sintering process. The washing treatment effectively reduced the leaching concentrations of Pb to agree the regulations. Therefore, water-washing followed by a sintering treatment is an available process for detoxifying the fly ash of MSWI.     

Reuse of cement-solidified municipal incinerator fly ash in cement mortars: physico-mechanical and leaching characteristics

The reuse of cement-solidified Municipal Solid Waste Incinerator (MSWI) fly ash (solidified/stabilised (S/S) product) as an artificial aggregate in Portland cement mortars was investigated. The S/S product consisted of a mixture of 48 wt.% washed MSWI fly ash, 20 wt.% Portland cement and 32 wt.% water, aged for 365 days at 20 degrees C and 100% RH. Cement mortars (water/cement weight ratio=0.62) were made with Portland cement, S/S product and natural sand at three replacement levels of sand with S/S product (0%, 10% and 50% by mass). After 28 days of curing at 20 degrees C and 100% RH, the mortar specimens were characterised for their physico-mechanical (porosity, compressive strength) and leaching behaviour. No retardation in strength development, relatively high compressive strengths (up to 36 N/mm2) and low leaching rates of heavy metals (Cr, Cu, Pb and Zn) were always recorded. The leaching data from sequential leach tests on monolithic specimens were successfully elaborated with a pseudo-diffusional model including a chemical retardation factor related to the partial dissolution of contaminant.     

Heavy metal removal from aqueous solutions by activated phosphate rock

The use of natural adsorbent such as phosphate rock to replace expensive imported synthetic adsorbent is particularly appropriate for developing countries such as Tunisia. In this study, the removal characteristics of lead, cadmium, copper and zinc ions from aqueous solution by activated phosphate rock were investigated under various operating variables like contact time, solution pH, initial metal concentration and temperature. The kinetic and the sorption process of these metal ions were compared for phosphate rock (PR) and activated phosphate rock (APR). To accomplish this objective we have: (a) characterized both (PR) and (APR) using different techniques (XRD, IR) and analyses (EDAX, BET-N(2)); and, (b) qualified and quantified the interaction of Pb(2+), Cd(2+), Cu(2+) and Zn(2+) with these sorbents through batch experiments. Initial uptake of these metal ions increases with time up to 1h for (PR) and 2h for (APR), after then, it reaches equilibrium. The maximum sorption obtained for (PR) and (APR) is between pH 2 and 3 for Pb(2+) and 4 and 6 for Cd(2+), Cu(2+) and Zn(2+). The effect of temperature has been carried out at 10, 20 and 40 degrees C. The data obtained from sorption isotherms of metal ions at different temperatures fit to linear form of Langmuir sorption equation. The heat of sorption (DeltaH degrees), free energy (DeltaG degrees) and change in entropy (DeltaS degrees) were calculated. They show that sorption of Pb(2+), Cd(2+), Cu(2+) and Zn(2+) on (PR) and (APR) an endothermic process. These findings are significant for future using of (APR) for the removal of heavy metal ions from wastewater under realistic competitive conditions in terms of initial heavy metals, concentrations and pH.     

Influence of flue gas SO2 on the toxicity of heavy metals in municipal solid waste incinerator fly ash after accelerated carbonation stabilization

The influence of CO₂ content and SO₂ presence on the leaching toxicity of heavy metals in municipal solid waste incinerator (MSWI) fly ash was studied by examining the carbonation reaction of MSWI fly ash with different combinations of simulated incineration flue gases. Compared with raw ash, the leaching solution pH of carbonated ash decreased by almost 1 unit and the leaching concentrations of heavy metals were generally lower, with that of Pb decreasing from 19.45 mg/L (raw ash) to 4.08 mg/L (1# carbonated ash). The presence of SO₂ in the incineration flue gas increased the leaching concentrations of heavy metals from the fly ash to different extents after the carbonation stabilization reaction. The pH of the leaching solution was the main factor influencing the leaching concentrations of heavy metals. The increase in buffer capacity with the pH of carbonated ash caused an increase in heavy metal stability after the carbonation reaction. Accelerated carbonation stabilization of MSWI fly ash could reduce its long-term leaching concentrations (toxicity) of Cu, Pb, Se, and Zn. The leaching concentrations of heavy metals from carbonated ash also likely had better long-term stability than those from raw ash. The presence of SO₂ in the incineration flue gas increased the proportion of exchangeable state species of heavy metals; slightly increased the long-term leaching toxicity of Cu, Pb, Se, and Zn; and reduced the long-term stability of these metals in the fly ash after the carbonation reaction.     

Sorption properties of the activated carbon-zeolite composite prepared from coal fly ash for Ni(2+), Cu(2+), Cd(2+) and Pb(2+)

Composite materials of activated carbon and zeolite have been prepared successfully by activating coal fly ash (CFA) by fusion with NaOH at 750 degrees C in N(2) followed by hydrothermal treatments under various conditions. Uptake experiments for Ni(2+), Cu(2+), Cd(2+) and Pb(2+) were performed with the materials thus obtained from CFA. Of the various composite materials, that were obtained by hydrothermal treatment with NaOH solution (ca. 4M) at 80 degrees C (a composite of activated carbon and zeolite X/faujasite) proved to be the most suitable for the uptake of toxic metal ions. The relative selectivity of the present sorbents for the various ions was Pb(2+)>Cu(2+)>Cd(2+)>Ni(2+), with equilibrium uptake capacities of 2.65, 1.72, 1.44 and 1.20mmol/g, respectively. The sorption isotherm was a good fit to the Langmuir isotherm and the sorption is thought to progress mainly by ion exchange with Na(+). The overall reaction is pseudo-second order with rate constants of 0.14, 0.17, 0.21 and 0.20Lg/mmol min for the uptake of Pb(2+), Cu(2+), Cd(2+) and Ni(2+), respectively.     

Biosorption of heavy metal ions on immobilized white-rot fungus Trametes versicolor

Trametes versicolor mycelia were immobilized in carboxymethylcellulose, CMC, beads via entrapment, and the bead containing immobilized fungus spores were incubated at 30 degrees C for 3 days to attain uniform growth on the bead surface. After incubation, the live and heat inactivated immobilized fungus on the CMC beads were used for the biosorption of Cu(2+), Pb(2+) and Zn(2+) ions.Plain CMC beads were used as a control system. The biosorption of Cu(2+), Pb(2+) and Zn(2+) ions by the CMC and both live and inactivated immobilized preparations increased as the initial concentration of Cu(2+), Pb(2+) and Zn(2+) ions in the medium increased. The maximum biosorption capacities for both immobilized live and heat inactivated Trametes versicolor were 1.51 and 1.84mmol Cu(2+), 0.85 and 1.11mmol Pb(2+) and 1.33 and 1.67mmol Zn(2+) per g of dry biosorbents, respectively. Biosorption equilibrium was established in about 1.0h and the equilibrium was well described by Langmuir and Freundlich isotherms. A temperature change in the range of 15-45 degrees C did not affect the biosorption capacity. The affect of pH was also investigated and the maximum adsorption of Cu(2+), Pb(2+) and Zn(2+) ions on the CMC and both live and inactivated immobilized fungal biomass was observed between pH 4.0 and 6.0. The CMC beads with the immobilized fungus can be regenerated using 10mM HCl, with up to 97% recovery of the metal ions; the biosorbents reused up to five biosorption-desorption cycles without any major loss in the biosorption capacity.     

Effects of water-washing pretreatment on bioleaching of heavy metals from municipal solid waste incinerator fly ash

Previous studies demonstrated that the bioleaching of municipal solid waste incinerator fly ash by Aspergillus niger was an efficient "green technology" for heavy metals removal, however, it demanded a long operational period. In this study, water-washing was used as a fly ash pretreatment before the bioleaching process (one-step and two-step). This pretreatment extracted 50.6% of K, 41.1% of Na, 5.2% of Ca and 1% of Cr from the fly ash. Due to the dissolution of alkali chlorides which hold particles together, fly ash particles were smashed into smaller granules by the hydraulic flushing action caused by vibration. After the pretreatment, the lag phase and bioleaching period were reduced by 45 and 30%, respectively, in one-step bioleaching of 1% (w/v) fly ash. Meanwhile, the metals extraction yield both in one-step and two-step bioleaching was increased markedly, e.g. in two-step bioleaching, 96% Cd, 91% Mn, 73% Pb, 68% Zn, 35% Cr and 30% Fe was extracted from 1% water-washed fly ash, respectively. The reduction of the bioleaching period and improvement of metals extraction yield will likely allow the practical application of the bioleaching technology for heavy metals removal from fly ash.     

Studies on sorption properties of zeolite derived from Indian fly ash

Indian fly ash has been completely converted to crystalline porous 13X zeolite by NaOH fusion at 600 degrees C followed by hydrothermal treatment at 105 degrees C for 20 h. Obtained materials were characterized by XRD, SEM and surface area measurement. Prepared material was used for the sorption study of different metal ions (Cu(2+), Co(2+) and Ni(2+)) at different pH, temperature. Thermodynamic data (DeltaS, DeltaH and DeltaG) corresponding to different metal ion uptake were evaluated from Langmuir equation. In all the experiment sorption capacity of prepared zeolite was found to be quite high than that of fly ash at acidic pH. However, the uptake selectivity order for both the materials is Cu(2+)>Co(2+)>Ni(2+).     

Melting of municipal solid waste incinerator fly ash by waste-derived thermite reaction

This work describes a novel approach for melting municipal solid waste incinerator (MSWI) fly ash, based on self-propagating reactions, by using energy-efficient simulated waste-derived thermite. The self-propagating characteristics, the properties of the recycled alloy and slag and the partitioning of heavy metals during the process are also studied. Experimental results demonstrate that the mix ratio of fly ash to the starting mixture of less than 30% supports the development of the self-propagating reaction with a melting temperature of 1350-2200 degrees C. Furthermore, metallic iron (or alloy) and the slag were retrieved after activation of the thermite reactions among the starting mixtures. It was noted that more than 91wt.% of iron was retrieved as alloy and the rest of non-reductive oxides as slag. During the thermite reactions, the partition of heavy metals to the SFA and flue gas varied with the characteristics of the target metals: Cd was mainly partitioned to flue gas (75-82%), and partition slightly increased with the increasing fly ash ratio; Pb and Zn, were mainly partitioned to the SFA, and the partition increased with increasing fly ash ratio; Cu was partitioned to the SFA (18-31%) and was not found in the flue gas; and moreover stable Cr and Ni were not identified in both the SFA and flue gas. On the other hand, the determined TCLP leaching concentrations were all well within the current regulatory thresholds, despite the various FA ratios. This suggests that the vitrified fly ash samples were environmental safe in heavy metal leaching. The results of this study suggested that melting of municipal solid waste incinerator fly ash by waste-derived thermite reactions was a feasible approach not only energy-beneficial but also environmental-safe.     

Behaviour of metals under the conditions of roasting MSW incinerator fly ash with chlorinating agents.

A total elemental analysis was performed on a municipal solid waste (MSW) fly ash sample, before and after it was treated at 1000 degrees C, to reveal the metal distribution between the volatile matter and the ash residue. Metals such as Pb, Zn, Cd, and to a lesser degree, Cr, Mn and Ni, were volatilized. Addition of chlorinating agents generally increased the volatility of certain elements. More acid resistant compounds were formed in the ash residue after the heat treatment using CaCl2 as a chlorinating agent. The efficiencies of volatilization of the metals, using Cl2 as a chlorinating agent, were generally higher compared with using CaCl2. However, CaCl2 was found to be a more selective chlorinating agent for volatilizing the heavy metals of concern, i.e., Pb, Cd, Zn and Cu. The efficiencies of volatilization of the recovered metals were approximately proportional to their standard free-energy changes (delta G(o) for the corresponding chlorination reactions.     

Disposal of MSWI fly ash through a combined washing-immobilisation process

The objective of this work was to investigate the feasibility of a combined washing-immobilisation process as a means of optimising the disposal of fly ash resulting from municipal solid waste incineration (MSWI) in cementitious matrices. Two different types of Italian MSWI fly ash and an ordinary Portland cement (ASTM Type I) were used. Washing pre-treatment of fly ash with water always produces a wastewater that can be successfully treated by reducing the pH to values of 6.5-7.5. This treatment is capable of removing the detected contaminants (Al, Cd, Pb, Zn) through two different mechanisms: precipitation of aluminium hydroxide and adsorption of cadmium, lead and zinc ions onto floc particles of Al(OH)(3). Setting and leaching tests on cementitious mixes prove that the hazardous sludge produced from wastewater treatment can be completely mixed with washed fly ash and this mixture can be incorporated into cementitious matrices to a great extent (75 wt.% of total solid) without the risks of an unacceptable delay of cement setting and an excessive heavy metals leachability from solidified products. The better performance of the combined washing-immobilisation process as compared to the immobilisation process of unwashed fly ash may be ascribed primarily to the ability of the washing step in promoting the formation of hydrate phases that incorporate and/or convert heavy metal compounds into less reactive forms and, secondarily, to its ability of removing significant amounts of alkali chlorides and sulphates from fly ash. As a result, MSWI fly ash is transformed into a material that adversely affects cement hydration to a much lower extent than unwashed fly ash.     

Characterisation of products of tricalcium silicate hydration in the presence of heavy metals

The hydration of tricalcium silicate (C(3)S) in the presence of heavy metal is very important to cement-based solidification/stabilisation (s/s) of waste. In this work, tricalcium silicate pastes and aqueous suspensions doped with nitrate salts of Zn(2+), Pb(2+), Cu(2+) and Cr(3+) were examined at different ages by X-ray powder diffraction (XRD), thermal analysis (DTA/TG) and (29)Si solid-state magic angle spinning/nuclear magnetic resonance (MAS/NMR). It was found that heavy metal doping accelerated C(3)S hydration, even though Zn(2+) doping exhibited a severe retardation effect at an early period of time of C(3)S hydration. Heavy metals retarded the precipitation of portlandite due to the reduction of pH resulted from the hydrolysis of heavy metal ions during C(3)S hydration. The contents of portlandite in the control, Cr(3+)-doped, Cu(2+)-doped, Pb(2+)-doped and Zn(2+)-doped C(3)S pastes aged 28 days were 16.7, 5.5, 5.5, 5.5, and <0.7%, respectively. Heavy metals co-precipitated with calcium as double hydroxides such as (Ca(2)Cr(OH)(7).3H(2)O, Ca(2)(OH)(4)4Cu(OH)(2).2H(2)O and CaZn(2)(OH)(6).2H(2)O). These compounds were identified as crystalline phases in heavy metal doping C(3)S suspensions and amorphous phases in heavy metal doping C(3)S pastes. (29)Si NMR data confirmed that heavy metals promoted the polymerisation of C-S-H gel in 1-year-old of C(3)S pastes. The average numbers of Si in C-S-H gel for the Zn(2+)-doped, Cu(2+)-doped, Cr(3+)-doped, control, and Pb(2+)-doped C(3)S pastes were 5.86, 5.11, 3.66, 3.62, and 3.52. And the corresponding Ca/Si ratios were 1.36, 1.41, 1.56, 1.57 and 1.56, respectively. This study also revealed that the presence of heavy metal facilitated the formation of calcium carbonate during C(3)S hydration process in the presence of carbon dioxide.     

A comparative study on Pb2+, Zn2+ and Cd2+ sorption onto zirconium phosphate supported by a cation exchanger

In the present study, a novel hybrid sorbent ZrP-001 was prepared by loading zirconium phosphate (ZrP) onto a strongly acidic cation exchanger D-001. Sorption behavior of Pb(2+), Zn(2+), and Cd(2+) onto ZrP-001 was experimentally examined by comparing with the host exchanger D-001. ZrP-001 was characterized by scanning electron micrograph (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), pH-titration and pore size distribution analysis. Sorption of the heavy metals onto ZrP-001 was found to be pH-dependent due to the ion exchange mechanism. Compared to D-001, a smaller pore size of ZrP-001 due to the ZrP dispersion consequently resulted in a lower sorption rate. Competitive effect of Ca(2+) on sorption of heavy metals onto ZrP-001 and D-001 was compared to elucidate sorption preference of the hybrid sorbent towards heavy metals. More favorable sorption of ZrP-001 than D-001 was observed for all the three metals and their sorption preference onto ZrP-001 followed the order Pb(2+)>Zn(2+) approximately Cd(2+). Fixed-bed sorption results and its efficient regeneration property further demonstrated that ZrP-001 is a potential candidate for removing heavy metals from contaminated water.