Stabilization/solidification of ashes in clays used in the manufacturing of ceramic bricks.

This paper presents the results of the lixiviation of metals from different mixtures of fly and bottom ashes that have been stabilized and solidified in clays used in the manufacture of bricks. The ashes used for this study were obtained from a Hoffmann-type brick furnace adapted for the incineration of municipal solid waste during the manufacturing of ceramic bricks. The ashes were stabilized in clay in different proportions of clay:ash mix (99:1, 95:5, 90:10, 80:20 and 60:40). Such mixes were used to manufacture bricks that were calcined at a temperature ranging from 50 to 1100 degrees C. The clay, ashes and manufactured bricks were characterized using X-ray diffraction, fluorescent X-ray, thermogravimetry, differential thermal analysis, atomic absorption spectroscopy and scanning electronic microscopy. In addition, toxicity characteristic leaching procedure lixiviation tests were performed according to the EPA 1311 method for the determination of heavy metals. The results showed an affinity between clay and ash, and also that the bricks manufactured with these mixtures present low lixiviation levels. The tests also showed the highest decrease in the concentration of arsenic, nickel, chromium, zinc and silver for 99:1 mixtures. The 95:5 mixture was found to be the most favourable for the stabilization (greater concentration decrease) of lead and cadmium. Selenium was the metal with the lowest concentration change whereas arsenic, nickel, chromium, zinc and cadmium showed the greatest concentration change in all mixtures, with the exception of cadmium in the mixture 99:1.     

Stabilization/solidification of waste ferrous sulphate from titanium dioxide production by fluidized bed combustion product

A treatment procedure to allow the disposal of waste ferrous sulphate was developed. This waste contains sulphuric acid and originates from titanium dioxide production. The process is based on simultaneous neutralization and stabilization/solidification (S/S) of the waste by means of fluidized bed combustion product (FBC-P). The prepared stabilized waste specimens have a solid matrix and their batch leachates display practically neutral pH and also satisfactory conductivity values. The leachate composition is notable in its absence of toxic metals and even iron.     

Stabilization/solidification of MSW incineration residues from facilities with different air pollution control systems. Durability of matrices versus carbonation

This paper discusses the stabilisation/solidification process with Portland cement applied to municipal solid waste incineration residues. Two types of residues were considered: fly ash (FA) produced in an electrostatic precipitator, and air pollution control (APC) residues from a semi-dry scrubber process. Cement pastes with different percentages of FA and APC residues were characterised according to their physical properties, the effect of the hydration products and their leaching behaviour. Portland pastes prepared with APC residues showed a rapid setting velocity in comparison with setting time for those pastes substituted with FA residues. Portland cement hydration was retarded in FA pastes. Leaching test results showed that heavy metals (such as Zn, Pb and Cd) and sulphates are immobilised within the paste, whereas chlorides are only partially retained. The carbonation process increases the leachability of S04(2-) and heavy metals such as Zn and Cr.     

Stabilization/solidification of fly ashes and concrete production from bottom and circulating ashes produced in a power plant working under mono and co-combustion conditions

Two combustion tests were performed in a fluidized bed combustor of a thermo-electric power plant: (1) combustion of coal; (2) co-combustion of coal (68.7% w/w), sewage sludge (9.2% w/w) and meat and bone meal (MBM) (22.1% w/w). Three samples of ashes (bottom, circulating and fly ashes) were collected in each combustion test. The ashes were submitted to the following assays: (a) evaluation of the leaching behaviour; (b) stabilization/solidification of fly ashes and evaluation of the leaching behaviour of the stabilized/solidified (s/s) materials; (c) production of concrete from bottom and circulating ashes. The eluates of all materials were submitted to chemical and ecotoxicological characterizations. The crude ashes have shown similar chemical and ecotoxicological properties. The s/s materials have presented compressive strengths between 25 and 40 MPa, low emission levels of metals through leaching and were classified as non-hazardous materials. The formulations of concrete have presented compressive strengths between 12 and 24 MPa. According to the Dutch Building Materials Decree, some concrete formulations can be used in both scenarios of limited moistening and without insulation, and with permanent moistening and with insulation.     

Toxicity mitigation and solidification of municipal solid waste incinerator fly ash using alkaline activated coal ash

Municipal solid waste (MSW) incineration is a common and effective practice to reduce the volume of solid waste in urban areas. However, the byproduct of this process is a fly ash (IFA), which contains large quantities of toxic contaminants. The purpose of this research study was to analyze the chemical, physical and mechanical behaviors resulting from the gradual introduction of IFA to an alkaline activated coal fly ash (CFA) matrix, as a mean of stabilizing the incinerator ash for use in industrial construction applications, where human exposure potential is limited. IFA and CFA were analyzed via X-ray fluorescence (XRF), X-ray diffraction (XRD) and Inductive coupled plasma (ICP) to obtain a full chemical analysis of the samples, its crystallographic characteristics and a detailed count of the eight heavy metals contemplated in US Title 40 of the Code of Federal Regulations (40 CFR). The particle size distribution of IFA and CFA was also recorded. EPA's Toxicity Characteristic Leaching Procedure (TCLP) was followed to monitor the leachability of the contaminants before and after the activation. Also images obtained via Scanning Electron Microscopy (SEM), before and after the activation, are presented. Concrete made from IFA, CFA and IFA-CFA mixes was subjected to a full mechanical characterization; tests include compressive strength, flexural strength, elastic modulus, Poisson's ratio and setting time. The leachable heavy metal contents (except for Se) were below the maximum allowable limits and in many cases even below the reporting limit. The leachable Chromium was reduced from 0.153 down to 0.0045 mg/L, Arsenic from 0.256 down to 0.132 mg/L, Selenium from 1.05 down to 0.29 mg/L, Silver from 0.011 down to .001 mg/L, Barium from 2.06 down to 0.314 mg/L and Mercury from 0.007 down to 0.001 mg/L. Although the leachable Cd exhibited an increase from 0.49 up to 0.805 mg/L and Pd from 0.002 up to 0.029 mg/L, these were well below the maximum limits of 1.00 and 5.00 mg/L, respectively.     

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.     

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.