Sulfur polymer solidification/stabilization of elemental mercury waste

Elemental mercury, contaminated with radionuclides, presents a waste disposal problem throughout the Department of Energy complex. In this paper we describe a new process to immobilize elemental mercury wastes, including those contaminated with radionuclides, in a form that is non-dispersible, will meet EPA leaching criteria, and has low mercury vapor pressure. In this stabilization and solidification process, elemental mercury is combined with an excess of powdered sulfur polymer cement (SPC) and sulfide additives in a mixing vessel and heated to approximately 40 degrees C for several hours, until all of the mercury is converted into mercuric sulfide (HgS). Additional SPC is then added and the temperature of the mixture raised to 135 degrees C, resulting in a molten liquid which is poured into a mold where it cools and solidifies. The final treated waste was characterized by powder X-ray diffraction and found to be a mixture of the hexagonal and orthorhombic forms of mercuric sulfide. The Toxicity Characteristic Leaching Procedure was used to assess mercury releases, which for the optimized process averaged 25.8 microg/l, with some samples being well below the new EPA Universal Treatment Standard of 25 microg/l. Longer term leach tests were also conducted, indicating that the leaching process was dominated by diffusion. Values for the effective diffusion coefficient averaged 7.6x10(-18) cm2/s. Concentrations of mercury vapor from treated waste in equilibrium static headspace tests averaged 0.6 mg/m3.     

Cement-clay pastes for stabilization/solidification of 2-chloroaniline

Immobilization of a model liquid organic pollutant, i.e. the 2-chloroaniline (2-CA), into a cement matrix using organoclays as pre-sorbent agents was investigated. Five cement-clay pastes were prepared with different nominal water-to-cement ratios (w/c=0.40, 0.25 and 0.15 wt/wt) and various amounts of waste (waste-to-cement o/c=0.20, 0.60 and 1.00 wt/wt); for comparison, a neat cement paste was also prepared. Dynamic leach tests were performed on solidified monoliths in order to assess the successful immobilization of the 2-CA. In monoliths at constant w/c ratio (0.40) the total amount of pollutant released increases with its initial content, and ranges from 15 to 35% with respect to it. By lowering w/c from 0.40 to 0.15 at constant o/c, the performances improved (<25% released). The microstructure of the hardened cement-clay pastes was characterized by quantitative X-ray diffraction (QXRD) and electronic microscopy (SEM-EDS) techniques; hydration degree was estimated by means of thermogravimetric analysis (TGA) in addition to QXRD. No evidence of any chemical reaction between 2-CA and cement phases was found. Moreover, it was shown that the most important factors affecting the cement hydration process were the total water content, i.e. the one taking also into account the water contained in the wet polluted clay, and the amount of 2-CA not firmly sorbed by the organoclay, and then freely dispersed in the paste.     

锑污染土壤固化-稳定化的影响因素

通过比较不同稳定剂、固化剂、土壤pH条件下土壤中重金属锑的修复效果,研究了锑的固化-稳定化影响因素并探讨了相关稳定化机理.实验结果表明:铁基稳定剂的效果明显优于磷酸二氢钾和腐殖酸钠,而零价铁的稳定化效果更优于硫酸铁和硫酸亚铁,较适宜的稳定剂投加量为5％(w);水泥做固化剂对锑的稳定化效果优于氧化钙,最佳投加量为5％(w...     

Cement‐based solidification/stabilization of phenol‐contaminated soil by bentonite and organophilic clay

The performance of ordinary and organophilic clays in the solidification and stabilization process was investigated with respect to the unconfined compressive strength (UCS) and leaching of phenol‐contaminated soil. The samples contained 2,000 mg/kg of phenol. White cement (15 and 30 percent by weight [wt%]) was used as binder, while ordinary and organophilic clays (8, 15, and 30 wt%) were applied as additives for reducing the harmful effects of phenol interference in cement hydration with a 28‐day curing time. The results revealed that the UCS is reduced by increasing the amount of clays. The values of UCS of all samples met the minimum standards specified for disposal in sanitary landfills determined by developed countries. The leaching test demonstrated that the degree of leaching diminished with increased clay content in all samples of both clay types. This reduction was observed to be greater in samples containing organophilic clay than in bentonite clay samples. Furthermore, the best composition of the materials tested was determined to be 30 wt% white cement plus 13.3 wt% organophilic clay with a compressive strength of 3,839 kPa, phenol removal percentage of 80 percent, and a cost of $67 per ton of contaminated soil.     

Optimization of cement-based stabilization/solidification of organic-containing industrial wastes using organophilic clays

The treatment of organically contaminated industrial wastes by cement-based stabilization/solidification has, in the past, been restricted by the detrimental effect of organic compounds on cement hydration. This work investigates the use of organophilic clays as adsorbents for the organic components of industrial wastes prior to conventional cement-based solidification. Three industrial wastes containing between 2–12% organic carbon and trace heavy metal contamination were treated with a quaternary ammonium salt exchanged clay. The organic component of all three wastes was well adsorbed by the clay. Solidification of the waste/clay mixes produced a monolithic mass with adequate strength and very low leaching of either the organic compounds or the metals. This study has shown that organophilic clays can act as successful adsorbents for the organic contaminants of industrial wastes and enable them to be treated by cement-based solidification.     

Cement-based solidification/stabilization of lead-contaminated soil at a utah highway construction site

This article describes portland cement-based solidification/stabilization (S/S) treatment of heavy metal-contaminated soil. The soil was discovered during highway construction in West Jordan, Utah. Environmental Chemical Corporation (ECC) performed an emergency response to remediate the soil under contract with the EPA and the United States Bureau of Reclamation (USBR). The soil was treated by S/S. Treatment of the soil, contaminated with lead and arsenic, involved: (1) excavation, (2) size segregation, (3) reduction of oversized particles, (4) addition and mixture of portland cement and cement kiln dust, and (5) beneficial reuse of the treated soil as a subbase. S/S treatment successfully reduced Toxicity Characteristic Leaching Procedure (TCLP) concentrations of the contaminants to below regulatory levels.     

Metal recovery from mine tailings using bacteria

Zinc metal and zinc sulfide were recovered by oxidative dissolution using Thiobacillus ferrooxidans, which is aerobic, autotrophic, and acidophilic bacteria. Thiobacillus ferrooxidans derive energy from oxidation of ferrous iron and elemental sulfur using molecular oxygen as an electron acceptor. From the 10, 000 mg/L of initial zinc concentration, 97% solubilization of zinc metal was obtained from coarse FeS₂ due to microbial action. Also, about 70% metal solubilization occurred with fine sized materials in 58 days. The general trend observed for the ZnS systems was a decrease in pH with time. The pH drop is an indication that microorganisms are acclimating and producing acidic by-products. The iron oxidation state changes due to substrate containing coarse particle size FeS₂ was shown. The shard drop of ratio of Fe(II)/Fe(Total) and sharp increase of ratio of Fe(III)/Fe(Total) was observed in 20 days after inoculation. Thus, microbial activity began more rapidly for the coarse particle size substrate than for the fine FeS₂.     

Laboratory stabilization/solidification of surrogate and actual mixed-waste sludge in glass and grout

Grout and glass formulations were developed for the stabilization of highly radioactive tank sludges. These formulations were tested in the laboratory with a surrogate and with a sample of an actual mixed waste tank sludge. The grout formulation was tested at wet-sludge loadings of 50–60 wt%, giving a volume increase of about 40–50 vol%. Dried sludge was vitrified into glass at waste oxide loadings of 40–50 wt%, giving a volume decrease of about 50–60 vol%. The Resource Conservation and Recovery Act (RCRA) metals included in surrogate testing were Ag, Ba, Cd, Cr, Ni, Pb, Se, Tl and Hg. Since vitrification would volatilize, not stabilize mercury, it was not included in the surrogates vitrified. The actual sludge sample was only characteristically hazardous for mercury by the toxic characteristic leaching procedure (TCLP) but exceeded the Universal Treatment Standard (UTS) limit for chromium. The grout and glass formulations stabilized these RCRA metals within UTS limits. In addition, a grout leachability index of about 9–10 was measured for both ⁸⁵Sr and ¹³⁷Cs, meeting the recommended requirement of >6. The glass leachability index was estimated to be >18 for cold cesium and strontium.     

Decomposition of hazardous organic materials in the solidification/stabilization process using catalytic-activated carbon

The application of a catalytic-activated carbon to the solidification/stabilization (S/S) process for immobilization of phenol and 2-chlorophenol and catalytic decomposition was investigated. The effect of the catalytic-activated carbon, in amounts of 0.25-1% (by dry sand wt.), on the leaching of phenol and 2-chlorophenol was studied. H2O2 was added as a source of oxygen in the amounts of 1 or 5%, with respect to liquid solution weight. Toxicity characteristic leaching procedure (TCLP) leaching tests showed that adding the catalytic-activated carbon to the S/S matrix significantly reduced the leachability of both phenol and 2-chlorophenol. Only trace amounts of phenol were found in the leaching solution, while the concentration of 2-chlorophenol was below the detection limit of the gas chromatography (GC). Without addition of the catalytic-activated carbon, 87% of the phenol and 92% of the 2-chlorophenol leached. Additional tests on TCLP leachate solutions using GC-mass spectrometry indicated the existence of simple, less hazardous, hydrocarbons, including alcohol. Catalytic-activated carbons treated with phenol in the presence of H2O2 were also analyzed using time of flight-secondary ion mass spectroscopy (TOF-SIMS). Results indicate that the phenol aromatic ring was broken by the catalytic reaction.     

Laboratory study on solidification/stabilization of unwanted medications using asphalt as a binder

The rise in discarded or unwanted medications (UMs) is becoming an issue of great concern, as it has the potential to harm the components of the environment where it is discarded: particularly air, water and soil. To combat this problem, many researchers have investigated the best approach for the collection and proper disposal of UMs. This paper intends to elaborate upon a safe solution for treating this waste, specifically through a process of solidification/stabilization (S/S) that involves mixing UMs with asphalt cement and asphalt concrete mixtures. Volumes of 5, 10, 15 and 20 % of a mixture of UMs were mixed with asphalt cement and the analyzed properties of the mixture of UMs–asphalt included: softening point, ductility, penetration, flash and fire points, specific gravity and rotational viscosity. Marshal stability, flow, air voids, unit weight, voids in mineral aggregate (VMA) and voids filled with binder (VFB) of asphalt concrete mixture were also investigated. Results showed that this approach of S/S is a promising method for dual achievements to solve an environmental problem and to use the waste for road construction.     

Study of the treatment effectiveness of a solidification/stabilization process for waste bearing heavy metals

The sludge from a steel processing unit bearing zinc, lead, iron, and manganese was solidified with ordinary Portland cement. The waste was stabilized in the specimens with a waste/binder ratio range of 0.16–4.0. On the basis of the available leaching and unconfined compressive strength, the performance of the solidified/stabilized waste was compared for different numbers of curing days. It was found that curing up to 28 days resulted in a performance improvement, as shown by less leaching of heavy metals and the increased unconfined compressive strength of the specimen. The treatment effectiveness of the solidification/stabilization process was assessed for the metals Pb, Zn, Fe, and Mn, and was found to be 89%, 95%, 74%, and 90%, respectively, for an optimum ratio of 4.0 after 28 days of curing.     

Petrographic and spectroscopic characterization of phosphate-stabilized mine tailings from Leadville,Colorado

The use of soluble PO4(3-) and lime as a heavy metal chemical stabilization agent was evaluated for mine tailings from Leadville, Colorado. The tailings are from piles associated with the Wolftone and Maid of Erin mines; ore material that was originally mined around 1900, reprocessed in the 1940s, and now requires stabilization. The dominant minerals in the tailings are galena (PbS), cerrusite (PbCO3), pyromorphite (Pb5(PO4)3Cl), plumbojarosite (Pb0.5Fe3(SO4)2(OH)6), and chalcophanites ((Pb,Fe,Zn,Mn)Mn2O5 x 2H2O). The tailings were treated with soluble PO4(3-) and lime to convert soluble heavy metals (principally Pb, Zn, Cu, Cd) into insoluble metal phosphate precipitates. The treatment process caused bulk mineralogical transformations as well as the formation of a reaction rind around the particles dominated by Ca and P. Within the mineral grains, Fe-Pb phosphosulfates, Fe-Pb sulfates (plumbojarosite), and galena convert to Fe-Ca-Pb hydroxides. The Mn-Pb hydroxides and Mn-(+/-Fe)-Pb hydroxides (chalcophanites) undergo chemical alteration throughout the grains during treatment. Bulk and surface spectroscopies showed that the insoluble reaction products in the rind are tertiary metal phosphate (e.g. (Cu,Ca2)(PO4)2) and apatite (e.g. Pb5(PO4)3Cl) family minerals. pH-dependent leaching (pH 4,6,8) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 150 for many metals; particularly Pb2+, Zn2+, Cd2+, and Cu2+. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca2+, PO4(3-) Pb2+, Zn2+, Cd2+, and Cu2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids.     

Incineration treatment of arsenic-contaminated soil

An incineration test program was conducted at the U.S. Environmental Protection Agency's Incineration Research Facility to evaluate the potential of incineration as a treatment option for contaminated soils at the Baird and McGuire Superfund site in Holbrook, Massachusetts. The purpose of these tests was to evaluate the incinerability of these soils in terms of the fate of arsenic and lead and the destruction of organic contaminants during the incineration process. The test program consisted of a series of bench-scale experiments with a muffle furnace and a series of incineration tests in a pilot-scale rotary kiln incinerator system. The study reported in this paper was funded by the Environmental Protection Agency under Contract 68–C9–0038 to Acurex Corporation. It has been subjected to the Agency's review and has been approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

Use of flue gas desulphurisation (FGD) waste and rejected fly ash in waste stabilization/solidification systems

Stabilization/solidification (S/S) processes have been used as the final treatment step for hazardous wastes prior to land disposal. Fly ash is a by-product of coal-fired power generation; a significant proportion of this material is low-grade, reject material (rFA) that is unsuitable as a cement replacement due to its high carbon content and large particle size (>45 microm). Flue gas desulphurization (FGD) sludge is a by-product from the air pollution control systems used in coal-fired power plants. The objective of this work was to investigate the performance of S/S waste binder systems containing these two waste materials (rFA and FGD). Strength tests show that cement-based waste forms with rFA and FGD replacement were suitable for disposal in landfills. The addition of an appropriate quantity of Ca(OH)2 and FGD reduces the deleterious effect of heavy metals on strength development. Results of TCLP testing and the progressive TCLP test show that cement-rFA-Ca(OH)2 systems with a range of FGD additions can form an effective S/S binder. The Leachability Index indicates that cement-based waste forms with rFA replacement were effective in reducing the mobility of heavy metals.     

Cement solidification of simulated off-gas condensates from vitrification of low-level nuclear waste solutions

Solidification in a cementitious matrix is a viable alternative for low-level nuclear waste management; it is therefore important to understand the behavior and properties of such wasteforms. We have examined the cementitious solidification of simulated off-gas waste streams resulting from the vitrification of low-level nuclear waste. Different possible methods for scrubbing the off-gasses from a vitrifier give rise to three possible types of waste compositions: acidic (from aqueous dissolution of volatile NOx and POx carried over from the vitrifier), basic (from neutralizing the former with sodium hydroxide), and fully carbonated (arising from a direct-combustion vitrifier). Six binder compositions were tested in which ordinary Portland cement was replaced at different proportions by fly ash and/or ground granulated blast furnace slag. A high solution to binder ratio of 1l/1 kg was used to minimize the volume of the wasteform and 10% attapulgite clay was added to all mixes to ensure that the fresh mix did not segregate prior to setting. The 28-day compressive strengths decreased when a high proportion of cement was replaced with fly ash, but were increased significantly when the cement was replaced with slag. The heats of hydration at early age for the various solids compositions decreased when cement was replaced with either fly ash or slag; however, for the fly ash mix the low heat was also associated with a significant decrease in compressive strength. High curing temperature (60 degrees C) or the use of extra-fine slag did not significantly affect the compressive strength. Recommendations for choice of binder formulations and treatment of off-gas condensates are discussed.     

Solidification/stabilization Process For Steel Foundry Dust Using Cement Based Binders: Influence Of Processing Variables

The influence of processing variables: mixing time, waste/binder ratio and water/solid ratio on the solidification/stabilization process of steel foundry dust has been studied. The characterization of the final product was based on the Toxic Characterization Leaching Procedure (TCLP) followed by the biotoxicity (bioluminescence assay) and concentration of the metals, Cr, Cd, Pb and Zn in the leachates. The final product characteristics depend mainly on the waste/binder ratio, as a function of the metal hydroxide solubilities. The results of this work allow one to establish the optimization of a solidification/stabilization process for steel foundry dust.     

Hybrid cement-assisted dewatering,solidification and stabilization of sewage sludge with high organic content

Sewage sludge with high organic content is particularly difficult to dewater before disposal in landfill. In this study, different hybrid cement binders were investigated to evaluate their ability to dewater the sewage sludge with high organic content. After 7 days of stabilization, the CASC (Mayenite/Sulfoaluminate cement) hybrid binder showed an excellent efficiency on both water content reduction and strength development; the water content and unconfined compressive strength value of solidified sludge reached 52.43 % and 109.55 kPa, respectively, at 8 % binder/sludge mass rate. The horizontal vibration leaching test (HJ 557-2009) indicated that leachability of heavy metals of the CASC-solidified sludge was far lower than that of non-solidified sludge and CAPC-solidified sludge. Furthermore, SEM and XRD analyses suggested that certain hydrates formed in the solidification process might have accelerated the depletion of interstitial water and strength development in the CASC-solidified sludge.     

A review on recent trends in solidification and stabilization techniques for heavy metal immobilization

Journal of Material Cycles and Waste Management - For environmental protection, safe disposal of toxic pollutants such as heavy metal is very important since they are regarded as hazardous waste....