Dennis G. Grubb

Assessment of cement kiln dust (CKD) for stabilization/solidification (S/S) of arsenic contaminated soils.

A stabilization/solidification (S/S) process for arsenic (As) contaminated soils was evaluated using cement kiln dust (CKD). Laboratory-prepared slurries, made of either kaolinite or montmorillonite, and field soils spiked with either As(3+) or As(5+) were prepared and treated with CKD ranging from 10 to 25 wt%. Sodium arsenite and sodium arsenate at 0.1 wt% were used to simulate arsenite (As(3+)) and arsenate (As(5+)) source contamination in soils, respectively. The effectiveness of treatment was evaluated at curing periods of 1- and 7-days based on the toxicity characteristic leaching procedure (TCLP). As-CKD and As-clay-CKD slurries were also spiked at 10 wt% to evaluate As immobilization mechanism using X-ray powder diffraction (XRPD) analyses. Overall, the TCLP results showed that only the As(5+) concentrations in kaolinite amended with 25 wt% CKD after 1 day of curing were less than the TCLP regulatory limit of 5mg/L. Moreover, at 7 days of curing, all As(3+) and As(5+) concentrations obtained from kaolinite soils were less than the TCLP criteria. However, none of the CKD-amended montmorillonite samples satisfied the TCLP-As criteria at 7 days. Only field soil samples amended with 20 wt% CKD complied with the TCLP criteria within 1 day of curing, where the source contamination was As(5+). XRPD and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) results showed that Ca-As-O and NaCaAsO(4).7.5H(2)O were the primary phases responsible for As(3+) and As(5+) immobilization in the soils, respectively.

Phosphate treatment of firing range soils: lead fixation or phosphorus release?

Phosphate treatment of lead (Pb)-contaminated soils relies on the premise that Pb converts to the thermodynamically stable, insoluble mineral class of pyromorphites. Recent research showed that treatment performance is kinetically controlled and strongly dependent on soil pH; this study employed an acidic phosphate (P) form, monobasic calcium phosphate (MCP), to investigate treatment performance of Pb occurring in an alkaline-buffered and an acidic firing range soil. The results of leaching, X-ray powder diffraction (XRPD), and modeling analyses showed that P and Pb dissolution in the alkaline soil and transformation reactions were kinetically controlled, so that: (i) TCLP (toxicity characteristic leaching procedure) and SPLP (synthetic precipitation leaching procedure) results were poor to marginal even at high MCP dosages; (ii) brushite (Ca(HPO(4)).2H(2)O) and cerussite (PbCO(3)) persisted in XRPD patterns; and, (iii) geochemical modeling failed to predict leaching and phase assemblages. In the acidic soil, Pb-P reactions promoted further soil acidification, improved TCLP performance, and generated better agreement with the equilibrium-based model; however, SPLP and modeling results showed that Pb concentrations could not be reduced below 15 microg/L mainly due to the low soil pH. The marginal or inadequate Pb immobilization was observed in both soils despite the elevated MCP dosages, which were well in excess of the pyromorphite stoichiometric ratio (P/Pb = 0.6). Additionally, P leaching concentrations and rates were extremely high (>300 mg/L), under both SPLP and deionized (DI) water extraction conditions, and as predicted by thermodynamic equilibrium. The performance and sustainability of phosphate-based treatment therefore seem questionable.

Stabilization/solidification of selenium-impacted soils using Portland cement and cement kiln dust.

Stabilization/solidification (S/S) processes were utilized to immobilize selenium (Se) as selenite (SeO(3)(2-)) and selenate (SeO(4)(2-)). Artificially contaminated soils were prepared by individually spiking kaolinite, montmorillonite and dredged material (DM; an organic silt) with 1000 mg/kg of each selenium compound. After mellowing for 7 days, the Se-impacted soils were each stabilized with 5, 10 and 15% Type I/II Portland cement (P) and cement kiln dust (C) and then were cured for 7 and 28 days. The toxicity characteristic leaching procedure (TCLP) was used to evaluate the effectiveness of the S/S treatments. At 28 days curing, P doses of 10 and 15% produced five out of six TCLP-Se(IV) concentrations below 10mg/L, whereas only the 15% C in DM had a TCLP-Se(IV) concentration <10mg/L. Several treatments satisfied the USEPA TCLP best demonstrated available technology (BDAT) limits (5.7 mg/L) for selenium at pozzolan doses up to 10 times less than the treatments that established the BDAT. Neither pozzolan was capable of reducing the TCLP-Se(VI) concentrations below 25mg/L. Se-soil-cement slurries aged for 30 days enabled the identification of Se precipitates by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX). XRD and SEM-EDX analyses of the Se(IV)- and Se(VI)-soil-cement slurries revealed that the key selenium bearing phases for all three soil-cement slurries were calcium selenite hydrate (CaSeO(3).H(2)O) and selenate substituted ettringite (Ca(6)Al(2)(SeO(4))(3)(OH)(12).26H(2)O), respectively.

Stabilized Dredged Material. I: Parametric Study

This study presents the results of a treatability study for dredged material (DM) stabilization using 20 combinations of pozzolanic agents (lime, cement kiln dust, high alkali and slag cements, and fly ash). The DM consisted of CH/OH soil excavated from the U.S. Army Corps of Engineers Craney Island confined disposal facility in Hampton Roads, Virginia, having an in situ moisture content of approximately 130% and void ratio of 3.35. Mix designs were prepared for each stabilized DM (SDM) blend using a 3-day mellowing period for the SDM blends to become compactable. Typical maximum dry unit weights were on the order of 11.9–12.9 kN/ m3 (76–82 lb/ ft3 ) , for total dry pozzolan doses to wet DM between 5 and 95%, the upper dosing limit being unconstrained for potential use of the SDM blends as fill. Unconfined compression strength (UCS) testing of the SDM blends using DM with an initial MC of 132.5% was completed in accordance with ASTM D1632 and ASTM D1633 for curing times of 7, 28, and 180 days. The 28-day ...

Importance of Mineralogy in the Geoenvironmental Characterization and Treatment of Chromite Ore Processing Residue

The geoenvironmental characterization of COPR at two deposition sites (New Jersey and Maryland) included geotechnical, chemical, mineralogical, and leaching analyses of three main chromite ore processing residue (COPR) types [gray-black (GB), hard brown (HB), clayey (C)]. Quantitative mineralogical analyses were instrumental in the delineation of the geochemical differences between the three COPR types, which enabled a framework to predict COPR response to potential remediation schemes. Overall, COPR mineralogy resembled cement, with hydration and pozzolanic reactions dominating its geochemistry. GB COPR was largely unreacted despite its prolonged exposure to humid conditions, while HB COPR was completely hydrated and contained high Cr(VI) concentrations. The two materials were chemically similar, with dilution accounting for the chemical and density differences. While the total acid neutralization capacity (ANC) of GB and HB was the same, the ANC at high pH (8–12) was higher in HB due to the dominance of...

Stabilized Dredged Material. III: Mineralogical Perspective

The prior two papers in this series reported on the geoenvironmental and geomechanical properties of 20 stabilized dredged material (SDM) blends using dredged material (DM) from the U.S. Army Corps of Engineers Craney Island confined disposal facility. The pozzolans included lime, cement kiln dust (CKD), class F fly ash, and two cements (portland and slag cement). This paper reports on the mineralogical evolution of the SDM blends over a 6-month curing period using techniques new to mainstream geotechnical engineering: X-ray diffraction (XRD) with Rietveld quantification analysis which allows direct quantitative mineralogical comparisons between soil samples. Despite being classified as a high plasticity clay-organic clay (CH/OH soil), XRD showed that the DM contained no montmorillonite, illite or kaolinite, and was thus mineralogically unreactive. The quartz, feldspar, and mica contents were numerically tracked and were shown to remain stable 6 months after blending. The chlorite (in DM) content decrease...

Stabilized Dredged Material. II: Geomechanical Behavior

This study presents the results of a detailed geotechnical evaluation of six stabilized dredged material (SDM) blends incorporating various combinations of lime, cement kiln dust, high alkali and slag cements, and Class F fly ash. The dredged material classified as CH/OH soil with an in situ moisture content (MC) of approximately 130% and void ratio of 3.35. Mix designs and unconfined compression strength tests were completed for each SDM blend based on 3-day mellowing characteristics. Compacted dry densities were on the order of 7.8–11.2 kN/ m3 ( 49–71 lb/ ft3 ) , with MCs on the order of 34–73%. Peak effective friction angles ranged from 20–50° with cohesion intercepts on the order of 30–235 kPa ( 4–34 lb/ in.2 ) using a maximum stress obiliquity criterion. Postpeak effective friction angles (15% axial strain) were routinely in excess of 40° with low cohesion ( <40 kPa ; 6 lb/ in.2 ). One sample exhibited very strong soil-fabric effects (cohesion) having an effective friction angle of only approximately...

DREDGED MATERIAL STABILIZATION: THE ROLE OF MELLOWING ON CURED PROPERTIES

This study presents the results of a treatability study for DM stabilization using fifteen combinations of stabilizing agents (lime, Cement Kiln Dust (CKD), fly ash). Two paste studies were conducted, both employing a mellowing period of up to 5 days under open and closed conditions, respectively. To illustrate the impacts of the different mellowing conditions on the characteristics of the stabilized DM, select physicochemical, geotechnical and mineralogical differences of the two sample sets are presented. Mellowing under closed conditions yielded non-compactable material for 10 of 15 blends, as the moisture content was too high. Conversely, open mellowing yielded compactable material for all blends as early as 2 days. The mineralogical analyses showed that cement reactions proceeded more slowly under closed conditions. Compaction curves generated for two blends under open and closed conditions yielded contradictory results in terms of blend performance, the higher densities being obtained under open conditions. Consequently, since open mellowing more closely resembles field conditions, it is recommended as a procedure prior to curing in future S/S paste studies.

Assessment of brownmillerite and periclase hydration in chromite ore processing residue at elevated temperature

Chromite ore processing residue (COPR) is a solid waste that was generated by the high temperature process of chromium extraction from chromite ore using soda ash and lime. The purpose of this study was to evaluate whether brownmillerite and periclase could be transformed into other minerals to understand and predict phase transformation during weathering in COPR. In this study, brownmillerite hydration to hydrogarnets and periclase to brucite in COPR materials were respectively assessed at elevated temperatures (100 o C and 200 o C) for 30 days because these reactions are very slow at ambient temperatures. The results showed that no apparent phase transformation was observed at 100 o C. However, brownmillerite and periclase started dissolving the first day at 200 o C, forming hydrogarnets and brucite, and completely dissolving after 15 days. Moreover, hydrogarnets were the main phase after 30 days of reaction. This indicated that the phase transformation could be possible when the initial COPR materials with high content of brownmillerite are exposed to long-term weathering.

Gowanus Canal Superfund Site. II: Stabilization/Solidification of MGP-Impacted Sediments

AbstractThe Gowanus Canal Superfund site is located in Brooklyn, New York. The sediment of the 2.9-km (1.8-mi) long canal is impacted at multiple locations by nonaqueous phase liquids (NAPLs) mainly from three historic manufactured gas plant (MGP) sites with measured NAPL saturations up to 50%. A stabilization/solidification (SS) treatability study was completed using 15 mix designs in a tiered testing suite that included unconfined compressive strength, hydraulic conductivity, and contaminant leach testing by equilibrium (as per U.S. EPA standard methods) and semidynamic leach methods, where semidynamic leach testing was modified with polydimethylsiloxane liners. Mix designs containing 5–10% (by dry weight) of a cement blend paired with 0.5% bentonite, or 1–4% organoclay added to wet NAPL-impacted sediments were characterized by unconfined compressive strength values greater and hydraulic condictivity values lower than 345 kPa (50 psi) and 1×10−6  cm/s, respectively. Leaching reductions for naphthalene (...