Frank K. Cartledge

Immobilization of As, Cd, Cr and PB-containing soils by using cement or pozzolanic fixing agents☆

The present work reports leaching data for a soil contaminated with four inorganic model wastes, Cd (II) and Pb (II) nitrates, sodium arsenite, and sodium chromate, at concentrations in the range of 10,000 to 12,200 ppm. Various combinations of Type I portland cement (OPC), Type F fly-ash, blast furnace slag, lime, and silica fume have been used to treat the contaminated soils, which are then leached using a slightly modified EP Tox1 leaching procedure. In no case does fly ash improve performance when mixed with other binding agents. Slag offers superior performance compared to fly ash in any combination tested and has some potential for general utility in practice. In particular, several mixtures including slag are effective in immobilizing lead, which sometimes given problems in solidification with cement. Type I portland is a very versatile and dependable reagent compared to the other agents used. In the cases of As and Cr, the performance of portland alone is superior to that of any other reagent or combination, when comparisons were made at the same dosage level. Cement alone was not among the fixing agents tested for Cd and Pb, but several combinations with cement were included. In every case, inclusion of OPC results in leachate concentrations as low as or lower than the corresponding mixture without OPC.

Solidification/stabilization of arsenic salts: Effects of long cure times

Abstract Leachability of As III and As V from various solidification-stabilization ( S S ) binders has been studied over a period of four years. Type I portland cement (OPC), both alone and mixed with a number of additives, results in toxicity characteristic leaching procedure (TCLP) leachabilities of ≤ 3 mg l −1 for arsenite and ≤ 2 mg l −1 for arsenate. There is no appreciable change in leachability after 3 years of cure, compared with 28 days of cure. The combination of OPC and Class F fly ash as a binder results in substantially degraded performance, as measured by TCLP leachability. Furthermore, the OPC-FA-As mixtures show increasing leachability with time. These solidified products have been studied using powder X-ray diffraction (XRD), derivative thermal gravimetry (DTG) and solid-state magic angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR). The As V salt, NaCaAsO 4 · 7.5H 2 O, is identifiable by XRD in many of these samples, particularly when sodium arsenate is the model As waste, but even when sodium arsenite is the original form of As. The OPC-FA mixtures show substantial respeciation during long curing times. There is evidence for formation of stratlingite from XRD, and there is substantial conversion of octahedrally coordinated aluminum, which is the predominant form at 28 days, to tetrahedrally coordinated aluminum at longer cure times, as shown by NMR. These matrix changes are correlated with increased leachability, although direct cause and effect cannot be established. These results emphasize the importance of long-term testing to identify specific combinations of S S binders and wastes that are prone to undergo respeciation, and consequent leachability changes, after long cure times.

Study by thermogravimetry of the evolution of ettringite phase during type II Portland cement hydration

Thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used by the authors as very effective tools to study hydration steps of cements used for solidification/stabilization of tanning wastes. The present paper presents a method which was applied to separate the peaks shown by DTG curves of type II Portland cement pastes, analyzed at different times during the first 4 weeks of setting. Through a specific software a more detailed study of the evolution of the cement hydration may be done, which allows the measurement of the amount of hydrated water present in tobermorite gel as well as in ettringite, which are the main phases formed from the original components of the cement. The number of moles of water present in the ettringite phase calculated by the method is in very good agreement with the values found in the literature, validating the method to calculate the same parameter in tobermorite gel. In the latter case the water content decreases significantly during the first day of hydration, then remains at a constant value over the rest of the analyzed period.

Characterization and phosphate stabilization of dusts from the vitrification of MSW combustion residues

Abstract The use of soluble PO 4 3− as a heavy metal chemical stabilization agent was evaluated for a dust generated from melting or vitrification of municipal solid waste combustion residues. Vitrification dusts contain high concentrations of volatile elements such as Cl, Na, K, S, Pb, and Zn. These elements are present in the dusts largely as simple salts (e.g. PbCl 2 , ZnSO 4 ) which are highly leachable. At an experimental dose of 0.4 moles of soluble PO 4 3− per kg of residue, the pH-dependent leaching (pH 5,7,9) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 100 for many metals; particularly Cd, Cu, Pb and Zn. Bulk and surface spectroscopies showed that the insoluble reaction products are tertiary metal phosphate [e.g. Zn 3 (PO 4 ) 2 ] and apatite [e.g. Pb 5 (PO 4 ) 3 Cl] family minerals. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca 2+ , Zn 2+ , Pb 2+ , Cu 2+ , and Cd 2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids. Soluble phosphate effectively converted soluble metal salts into insoluble metal phosphate phases despite the relatively low doses and dry mixing conditions that were used. Soluble phosphate is an effective stabilization agent for divalent heavy metals in melting dusts where leachable metals are present in high concentrations.

Stereochemistry of reactions in the 1,2-dimethylsilacyclopentane ring system. II. Stereoselective transformation

Abstract Preparations, separations of geometric isomers, and structural assignments based on nmr and on chemical evidence are described for a number of 1-substituted 1,2-dimethylsilacyclopentanes. A number of stereospecific reactions have been observed, and the stereochemistry is in all cases the same as that observed for acyclic silanes. A discussion of the role of ring strain in determining stereochemical outcome and reaction rates is presented.

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.

State of the art on stabilization of hazardous organic liquid wastes and sludges

The principal motivation for undertaking this study was to examine stabilization techniques to determine the technical feasilibity of stabilizing/solidifying organic liquid wastes and sludges. The performance of the processes must often be judged on the basis of the manufacturers claims rather than the evaluation of an impartial referee. The study was largely concerned with documenting the state‐of‐the‐art and identifying promising directions for additional research. The most recent available literature, supplemented by telephone contacts with vendors and companies, were the primary information sources. Based on an exhaustive search of the research literature dealing with the solidification and stabilization of hazardous organic wastes, the following observations can be made: (1) Few adequately documented studies have been reported on the performance (physical and chemical stability) of solidified and/or stabilized mixtures containing hazardous organic wastes. (2) Almost no published information exists o...

Evaluating cement hydration by non-conventional DTA; An Application to Waste Solidification

This paper presents a method to study cement hydration at ambient temperatures by using a micro processed non-conventional differential thermal analysis (DTA) system, which was used to evaluate the solidification/stabilization process of tannery wastes produced in the leather industry. The DTA curves of pastes composed by slag cement, Wyoming bentonite and waste are obtained in real time and used to analyze the heat effects of the reactions during the first 24 h of hydration. By applying a deconvolution method to separate the overlapped DTA peaks, the energy released in the several hydration stages may be estimated and consequently, the effects of each component on the solidification process. The highest separated DTA peak occurs during the several early stages of cement hydration and is due mainly to tricalcium silicate hydration. Very good correlation shows that the greater is the waste content in the paste composition, the higher is its effect on the rates of reactions occurring during the induction (dormant) period of cement hydration. The presence of bentonite used as a solidification additive in the stabilization process has a similar but less dramatic effect on the dormant period.

Solvent-catalyzed cis-trans isomerization of halosilacyclo-butanes and -pentanes. Evidence for cationic intermediates with expanded coordination

Abstract 1-Chloro-l,2,-dimethylsilacyclo-butane (IV)and-pentane (V) undergo cis-trans isomerization catalyzed by a variety of nucleophilic species, including polar aprotic solvents. Kinetics of the process have been investigated for HMPT in CCl4. Rate laws and the observation of HMPT-catalyzed halogen exchange between bromo- and chloro-silanes lead to the conclusion that 5-coordinate siliconium ions are intermediates in this process. Evidence is also presented that pentacoordinate species formed from V (but not from IV) undergo rapid pseudorotations.

A preliminary assessment of the use of an amorphous silica residual as a supplementary cementing material

An amorphous silica (AS) by-product was investigated as a possible supplementary cementing material (SCM). Standard ASTM tests for the SCM as well as specific surface area measurement, electron microscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (SRD), {sup 29}Si nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, and cement paste and mortar cube strength studies were conducted. A 10:90 AS:OPC paste (w/cm of 0.4) and mortar cubes (w/cm = 0.50 to 0.60) were prepared. AS is a white amorphous material ({bar x}=29{+-}9(1{sigma}) nm) with a surface area of 95,000 m{sup 2}/kg, the latter resulting in a high water demand. All of the AS in 10:90 AS:OPC paste reacted by 7 days, consuming more than 50% of the calcium hydroxide. The compressive strength of OPC paste remained unchanged with the addition of AS but that of mortar increased.