Immobilization of copper ions laden kaolin waste: influence of thermal treatment on its immobilization in cement paste

This work aims to study the influence of thermal treatment of Cu²⁺ laden kaolin wastes on its immobilization efficiency in cement paste. Compressive strength and toxicity characteristic leaching procedure (TCLP) of 5–20 % kaolin waste blended cement pastes were tested. X-ray diffraction (XRD) results illustrate that adsorption of Cu²⁺ ions modify the crystal structure of kaolinite mineral. Fourier transform infrared (FTIR) results indicate that the adsorption sites on the kaolin surface that were occupied with free water molecules have been replaced with Cu²⁺ ions adsorbed from aqueous solutions. The thermal treatment of kaolin waste improves fixation ratio of Cu²⁺ in cement pastes containing up to 20 % of thermally treated waste. This is due to: pozzolanic activity of calcined kaolin, conversion of leachable adsorbed Cu²⁺ ions into encapsulated unleachable phase that does not retard the hydration of cement as well as adsorption of much of leachable Cu²⁺ ions on surfaces of hydration products and occlusion in its lattice structure as illustrated from XRD, FTIR, thermogravimetric, scanning electron microscopy and TCLP results. The fixation ratio of Cu²⁺ in cement paste blended with 20 % of thermally treated kaolin waste, reaches maximum value of about 97 % compared to 82 % for cement paste blended with 20 % of untreated kaolin waste.     

Long-term leaching scenarios for cement-based waste forms

Cement-based waste forms (solidified wastes) are used for the long-term land disposal of industrial hazardous wastes. A cement-based waste form can be prepared by mixing a hydraulic cement and, if needed, a bulking agent with an aqueous waste to cause it to solidify.This article presents eight long-term leaching scenarios based on various properties of waste forms and contaminants as well as different hydraulic regimes and characteristics of groundwater. Each scenario takes the form of a simplified mathematical model used to predict leaching rates for periods of up to 100 years.The analysis demonstrates the importance of chemically fixing the contaminants in the matrix and illustrates the advantages of avoiding situations where ground-water flows through the waste. In situations where advective transport is negligible, leaching rates are limited by pore diffusion and tend to decrease with time.     

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.     

An alternative method for the treatment of waste produced at a dye and a metal-plating industry using natural and/or waste materials.

The aim of this study was to develop cost-effective, appropriate solidification technologies for treating hazardous industrial wastes that are currently disposed of in ways that may threaten the quality of local groundwater. One major objective was to use materials other than cement, and preferably materials that are themselves wastes, as the solidification additives, namely using wastes to treat wastes or locally available natural material. This research examines the cement-based and lime-based stabilization/solidification (S/S) techniques applied for waste generated at a metal-plating industry and a dye industry. For the lime-based S/S process the following binder mixtures were used: cement kiln dust/ lime, bentonite/lime and gypsum/lime. For the cement-based S/S process three binder mixtures were used: cement kiln dust/cement, bentonite/cement and gypsum/cement. The leachability of the wastes was evaluated using the toxicity characteristic leaching procedure. The applicability and optimum weight ratio of the binder mixtures were estimated using the unconfined compressive strength test. The optimum ratio mixtures were mixed with waste samples in different ratios and cured for 28 days in order to find the S/S products with the highest strength and lowest leachability at the same time. The results of this work showed that the cement-and lime-based S/S process, using cement kiln dust and bentonite as additives can be effectively used in order to treat industrial waste.     

Examination of the influence of dissolved halite (NaCl) on the leaching of lead (Pb) from cement-based solidified wastes

The leaching of lead from cement-based solidified waste forms mixed at different water/cement ratios was studied by conducting equilibrium and semi-dynamic leaching tests using deionized water and sodium chloride solutions. The results suggest that leaching of the primary constituents of the cement (calcium, silicon and sulfate) is controlled by solubility equilibria, with increased leaching into chloride solutions due to ionic strength effects. The original porosity of the waste forms increased with water/cement ratio and chloride solutions further increased it as a result of decalcification. Lead leaching was generally low, and appears to be a transport-controlled process, such that leaching correlates positively with porosity.     

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.     

Chemical fixation,solidification of hazardous waste

Efficient, cost effective measures for the safe disposal of hazardous wastes have been developed to meet the needs of industries in Brisbane and the surrounding area. Liquid hazardous wastes are neutralised, oxidised, or reduced as appropriate, and fixed (solidified) by the addition of fly-ash and cement kiln dust to form a material of the consistency of coarse gravel. Fixation is performed in cells dug in solid clay, holding about 70 tonnes. Fixed material containing pesticides, paints or organic solvents is left in the clay cells, capped with clay; fixed inorganics and waste oils having no toxic contaminants are used for land contouring on the site. Leachate tests on the latter have been uniformly below 10 times USEPA Drinking Water guidelines — that is, 10 times better than the limits nominated by the EP Leach Test (1980). Bores around the site have detected no leachates during the past seven years. A simple but effective management system keeps wastes segregated and confirms the identity of each batch of waste on receipt. All costs are charged to the waste generator including costs of correcting errors.     

Use of mix of clay/solid waste from steel works for civil construction materials.

The present study focuses on the use of solid waste generated by the steel works in Brazil for manufacturing clay-based structural products. The waste sample was characterized regarding chemical composition, X-ray diffraction, particle size, morphology, specific surface and plastic properties. The waste was added in gradual proportions to a kaolinitic clay from zero up to 3 wt.%. Ceramic bodies were formed by vacuum extrusion and fired at 950 degrees C. The physical-mechanical properties (linear shrinkage, water absorption, apparent density and flexural strength) of the resulting clay/solid waste mixtures were determined. In addition, leaching tests were performed according Brazilian Standards as well as a preliminary analysis of gases evolved during the thermal process. It was found that the solid waste is formed by irregular particles, ranging in size from 1 to 500 microm. The test results indicate that solid wastes generated by steel works can be used as filler in construction materials, thereby increasing reuse in an environmentally safe manner.     

Improvement of nuclide leaching resistance of paraffin waste form with low density polyethylene

Low-level liquid borate wastes have been immobilized with paraffin wax using a concentrate waste drying system (CWDS) in Korean nuclear power plants. The possibility for improving chemical durability of paraffin waste form was suggested in this study. A small amount of low density polyethylene (LDPE) was added to increase the leaching resistance of the existing paraffin waste form. The influence of LDPE on the leaching behavior of waste form was investigated by performing leaching test according to ANSI/ANS-16.1 procedure during 325 days. It was observed that the leaching of nuclides immobilized within paraffin waste form made a marked reduction although little content of LDPE was added to waste form. The acceptance criteria of paraffin waste form associated with leachability index (LI) and compressive strength after the leaching test were fully satisfied with the help of LDPE.     

Stabilization of chloro-organics using organophilic bentonite in a cement-blast furnace slag matrix.

The application of cement-based stabilisation/solidification treatment to organic-containing wastes is made difficult by the adverse effect of organics on cement hydration. The use of organophilic clays as pre-solidification adsorbents of the organic compounds can reduce this problem because of the high adsorption power of these clays and their compatibility with the cementitious matrix. This work presents an investigation of the effect on hydration kinetics, physico-mechanical properties and leaching behaviour of cement-based solidified waste forms containing 2-chlorophenol and 1-chloronapthalene adsorbed on organophilic bentonites. These were prepared by cation exchange with benzyldimethyloctadecylammonium chloride and trimethyloctadecylammonium chloride. The binder was a 30% pozzolanic cement, 70% granulated blast furnace slag mixture. Several binder-to-bentonite ratios and different concentrations of the organics on the bentonite were used. Kinetics of hydration were studied by measurement of chemically bound water and by means of thermal and calorimetric analyses. Microstructure and other physico-mechanical properties of the solidified forms were studied by means of mercury intrusion porosimetry, scanning electron microscopy and unconfined compressive strength measurement. Leaching was checked by two different leaching tests: one dynamic, on monolithic samples, and the other static, on powdered samples. This study indicates that the incorporation of the organic-loaded bentonite in the binder matrix causes modifications in the hardened samples by altering cement hydration. The effects of the two organic contaminants are differentiated.     

Recycling MSWI bottom and fly ash as raw materials for Portland cement

Municipal solid waste incineration (MSWI) ash is rich in heavy metals and salts. The disposal of MSWI ash without proper treatment may cause serious environmental problems. Recently, the local cement industry in Taiwan has played an important role in the management of solid wastes because it can utilize various kinds of wastes as either fuels or raw materials. The objective of this study is to assess the possibility of MSWI ash reuse as a raw material for cement production. The ash was first washed with water and acid to remove the chlorides, which could cause serious corrosion in the cement kiln. Various amounts of pre-washed ash were added to replace the clay component of the raw materials for cement production. The allowable limits of chloride in the fly ash and bottom ash were found to be 1.75% and 3.50% respectively. The results indicate that cement production can be a feasible alternative for MSWI ash management. It is also evident that the addition of either fly ash or bottom ash did not have any effect on the compressive strength of the clinker. Cement products conformed to the Chinese National Standard (CNS) of Type II Portland cement with one exception, the setting time of the clinker was much longer.     

Accelerated carbonation treatment of industrial wastes

The disposal of industrial waste presents major logistical, financial and environmental issues. Technologies that can reduce the hazardous properties of wastes are urgently required. In the present work, a number of industrial wastes arising from the cement, metallurgical, paper, waste disposal and energy industries were treated with accelerated carbonation. In this process carbonation was effected by exposing the waste to pure carbon dioxide gas. The paper and cement wastes chemically combined with up to 25% by weight of gas. The reactivity of the wastes to carbon dioxide was controlled by their constituent minerals, and not by their elemental composition, as previously postulated. Similarly, microstructural alteration upon carbonation was primarily influenced by mineralogy. Many of the thermal wastes tested were classified as hazardous, based upon regulated metal content and pH. Treatment by accelerated carbonation reduced the leaching of certain metals, aiding the disposal of many as stable non-reactive wastes. Significant volumes of carbon dioxide were sequestrated into the accelerated carbonated treated wastes.     

Prediction of unconfined compressive strength of cement paste containing industrial wastes

Neural network analysis was used to construct models of unconfined compressive strength (UCS) as a function of mix composition using existing data from literature studies of Portland cement containing real industrial wastes. The models were able to represent the known non-linear dependency of UCS on curing time and water content, and generalised from the literature data to find relationships between UCS and quantities of five waste types. Substantial decreases in UCS were caused by all wastes; except for EAF dust, the effect was nonlinear with the greatest decrease caused initially by approx. 12% plating sludge, 40% foundry dust, 58% other ash, and 72% MSWI fly ash by mass of dry product. It appears that the maximum waste additions used in modelling may approximate the practical limits of waste additions used in modelling may approximate the practical limits of waste addition to Portland cement, i.e., 50% plating sludge or EAF dust, 64% foundry dust, 92% other ash, and 85% MSWI fly ash by mass of dry product. The laboratory was found to be a key predictive variable and acted as a surrogate for laboratory-specific variables related to cement composition, strength and hardening class, product mixing and preparation details, laboratory conditions, and testing details. While the neural network modelling approach has been shown to be feasible, development of better models would require larger data sets with more complete information regarding laboratory-specific variables and waste composition.     

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.     

Reduction of natural resource consumption in cement production in Japan by waste utilization

According to Japanese government policy, the input of natural resources should be minimized and input resources should be utilized to the greatest extent possible so that, eventually, minimum waste is generated. The cement industry of Japan has worked hard to maximize waste utilization. Focusing on the cumulative amounts of the elements needed for clinker and gross calorific values, this study estimated the extent to which waste utilization has directly or indirectly reduced natural resource consumption and greenhouse gas emissions associated with cement production at 32 factories in Japan and clarified the effect of waste utilization in the cement industry on the resource productivity of Japan based on information for fiscal year 2008. Had no wastes been utilized, the cement industry consumption of limestone would have been 18% higher; of clay, 2,899% higher; and of energy, 22% higher. The utilization of wastes in the mixing and burning process of cement production directly reduced greenhouse gas emissions (12% emitted gas reduction) by a larger amount than the indirect reduction achieved by their utilization during the admixing process (10% reduction). Waste utilization for cement production contributed to an increase in resource productivity of about 8,000 Japanese Yen/ton.     

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.     

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.     

Modelling the effects of waste components on cement hydration

Ordinary Portland Cement (OPC) is often used for the solidification/stabilization (S/S) of waste containing heavy metals and salts. These waste components will precipitate in the form of insoluble compounds on to unreacted cement clinker grains preventing further hydration. In this study the long term effects of the presence of contaminants in solidified waste is examined by numerically simulating cement hydration after precipitation of metal salts on the surface of cement grains. A cement hydration model was extended in order to describe pore water composition and the effects of cement grain coating. Calculations were made and the strength development predicted by the model was found to agree qualitatively with experimental results found in literature. The complete model is useful in predicting the strength and leaching resistance of solidified products and developing solidification recipes based on cement.     

Leaching characteristics of paraffin waste forms generated from Korean nuclear power plants

Leaching tests of paraffin waste forms including boric acid, cobalt, strontium and cesium were performed to investigate the leaching characteristics of paraffin waste forms which had been generated in Korean nuclear power plants. The leaching tests were conducted according to ANSI/ANS-16.1 test procedure and the cumulative fractions leached (CFLs) of boric acid, cobalt, strontium and cesium were obtained. The compressive strength before and after the leaching test was measured for various waste forms with different mixing ratios of boric acid to paraffin. It was observed that boric acid and other nuclides immobilized within paraffin waste forms were congruently released and the leaching rates were influenced by reacted layer depth as the dissolution reaction progressed. A shrinking core model based on the diffusion-controlled dissolution kinetics was developed in order to simulate the test results. The CFLs and the leaching rates were well expressed by the shrinking core model and the cross-sectional view of specimen after the test demonstrated the applicability of this model with the shrinking dissolution front to the leaching analysis of paraffin waste forms.     

Recycling municipal incinerator fly- and scrubber-ash into fused slag for the substantial replacement of cement in cement-mortars

Fly- and scrubber-ash (weight ratio of approximately 1:3) from municipal solid waste incinerators (MSWI) are a major land-fill disposal problem due to their leaching of heavy metals. We uniformly mixed both types of ash with optimal amounts of waste glass frit, which was then melted into a glassy slag. The glassy slag was then pulverized to a particle size smaller than 38 μm for use as a cement substitute (20–40% of total cement) and blended with sand and cement to produce slag-blended cement-mortar (SCM) specimens. The toxicity characteristics of the leaching procedure tests on the pulverized slag samples revealed that the amount of leached heavy metals was far below regulatory thresholds. The compressive strength of the 28-day cured SCM specimens was comparable to that of ordinary Portland cement mortars, while the compressive strength of specimens cured for 60 or 90 days were 3–11% greater. The observed enhanced strength is achieved by Pozzolanic reaction. Preliminary evaluation shows that the combination of MSWI fly- and scrubber-ash with waste glass yields a cost effective and environmentally friendly cement replacement in cement-mortars.