Pedro M. Büchler

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.

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.

Sorption of oil pollution by organoclays and a coal/mineral complex

Recently, increasing concern about pollution of groundwater by organic chemicals has led to research on the use of various adsorbents. This study addressed the sorption of phenol and organic compounds by two organoclays and a coal/mineral complex (ARO). The organoclays used were a bentonite from Brazil (SVC) and Wyoming bentonite (SWy) with quaternary ammonium salt (ABDMA). Swelling capacity of the sorbents in toluene, diesel, gas, Varsol and kerosene were measured. Absorption of organic compounds served as an ASTM D 281-95 base, which resulted in the following order for ABDMA-SVC: gas > toluene > kerosene > diesel > Varsol. ABDMA-SWy absorbed in the following order: gas > toluene > Varsol > diesel > kerosene. ARO absorbed: gas > toluene >diesel > Varsol > kerosene. Sorption of phenol followed the order of ABDMA-SVC > ABDMA-SWy > ARO. The adsorption data show that the materials prepared were effective in sorbing phenol, and that the Brazilian clay was the most efficient of the three materials.

The Effect of Different Bentonites on Cement Hydration During Solidification/Stabilization of Tannery Wastes

In the present work, a Portland cement blended with calcium carbonate is being used to study the solidification/stabilization (S/S) of a Brazilian tanning waste arising from leather production. Chromium is the element of greatest concern in this waste, but the waste also contains a residual organic material. Using thermogravimetry (TG) and derivative thermogravimetry (DTG) to identify and quantify the main hydrated phases present in the pastes, this paper presents a comparative study between the effects of Wyoming and Organophilic bentonites (B and OB) on cement hydration. Samples containing combinations of cement, B, OB and waste have been subjected to thermal analysis after different setting times during the first 28 days of the waste S/S process. Both bentonites affect the cement hydration, with no significant differences in hydration degree after 1 week. This work shows further examples of the great utility of thermal analysis techniques in the study of very complex systems containing both crystalline and amorphous mineral materials as well as organics.

Solidification/stabilization of a tannery waste with blended cement and wyoming bentonite

Abstract The solidification/stabilization of a tannery waste, which has a high chromium content, was studied by thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA). Pastes prepared with water, cement, tannery waste and Wyoming bentonite were analyzed after different setting times during the first 28 days of solidification. In the present work it is clear that Wyoming bentonite combined with waste affects cement hydration, while bentonite alone does not affect it significantly. The presence of the waste results in a small acceleration of the cement hydration reactions, probably due to the presence of extra Ca and alkalinity in the waste. When waste is present in the sample during TG and DTG analysis, it is burned to carbon dioxide, which partially reacts with the calcium hydroxide formed during cement hydration. This results in an underestimate of the calcium hydroxide content of the solidified sample. The greater the degree of hydration of the waste‐containing cement sample, the greater the amount of carbon dioxide absorbed.

Solidification/stabilization of arsenic : Effects of arsenic speciation

Abstract Chemical identity of arsenic compounds subjected to solidification/stabilization (S/S) is a major factor in determining eventual leachability from the treated material. When several arsenic compounds were treated with portland cement under the same conditions, Toxicity Characteristic Leaching Procedure (TCLP) leachability of arsenic after 28 days of cure ranged from 510 mg/L for arsanilic acid to 1.7 mg/L for sodium arsenate. The arsenic compounds also have major effects on cement hydration reactions, as shown in solid‐state NMR spectra, but there is not a direct correlation between degree of hydration in the matrix and arsenic leachability; indeed, the most leachable arsenic compound studied, arsanilic acid, shows the least effect on cement hydration. A commercial organoarsenic fungicide waste was treated with portland cement alone and in the presence of tetramethylammonium bentonite. Inclusion of the organoclay reduced arsenic leachability by a factor of 5–6.

Thermal Analysis of Municipal Sludge Waste Combustion

Municipal sludge waste combustion was studied by thermogravimetry (TG) and differential thermal analysis (DTA), to better understand the two main stages which occur during the combustion process, and to evaluate how much of the total and significant generated heat is released is during each combustion stage. A method to measure the lower heating value (LHV) on a dried basis was developed from the TG/DTA data and it was applied to the whole process and to each combustion stage. Chemical analysis of the residual products after each step shows that nitrogen organic compounds are burnt only from 350°C to 550°C, and that the organics which are released and burnt in the previous step, which begins by 150°C, present a heating value of about 32MJ/kg. The nitrogen containing compounds present a lower LHV.

Tannery waste solidification and stabilization

The stabilization/solidification of tannery waste containing chromium was studied as an option for its treatment and final disposal, by using a Portland cement type II and two different commercial bentonites (sodium and organophilic) as additives. Different compositions were evaluated by compressive strength analysis, porosity measurement, leaching tests and thermal analysis. The effect on the compressive strength is directly related to the resulting effect of the components present in the original paste on the hydration degree of the cement, which can be evaluated by thermogravimetric analysis from the dehydration steps of tobermorite and ettringite phases of the pastes. The results show that this process is suitable for the treatment of the tanning waste and that the best conditions of stabilization are obtained when both additives are used.

Modification of Mackinawite with L-Cysteine: Synthesis, Characterization, and Implications to Mercury Immobilization in Sediment

Environmental remediation of mercury contaminated sediment includes the inhibition or minimization of mercury methylation. Mackinawite (FeS) is an excellent material that inhibits mercury methylation (Liu et al, 2009). Effective remediation of sediment contaminated with mercury is essential in minimizing the contamination of fish and shellfish and, consequently, the human exposure to methyl mercury. In-situ capping (ISC) is one of the remediation methods that have been found to reduce the mercury transport from sediment to the overlying water. It consists of placing a proper layer of isolating material between the layers of contaminated sediment and overlying water (Palermo, 1998; Liu et al., 2007). This method is attractive due to the reduction in mobility and availability of the contaminant, and requires fewer infrastructures associated with handling, dewatering, treatment and disposal. Mackinawite was reported as an effective isolating material for use as a sediment cap (Liu et al, 2009). Although pure mackinawite can immobilize mercury, it has a low stability when exposed to oxidized conditions (Burton et al, 2009; Liu et al, 2008; Wolthers et al, 2005). Under field conditions, the capping material has to be in contact with the oxigenated water column during the capping building. This process can oxidize the mackinawite, making this material unable to reacting with the contaminant. Therefore, is important to make the FeS more resistant to oxidation. To obtain stable mackinawite, we proposed to modify its surface using L-cysteine as an organic ligand, considering ferredoxin as a model. Ferredoxins are proteins that have an inorganic active core constituent of Fe2S2 or Fe4S4 bonded to L-cysteine groups. This core participates in electron-transfer, contributing to important biological functions such as respiration and photosynthesis (Fontecave and Ollagnier-de-Choudens,

An Experimental Study of Sewage Sludge Incineration

Sludge incinerated ash has been fired at different temperatures. This material was fired at 1050 °C for 3 h and until a peak of 1010°C. After thermal treatment the ash was screened at 200 mesh. The ash was characterized by X-ray fluorescence and trace elements like Cr, Pb, Zn, Cu, and some oxides like quartz(SiO2), Al2O3, P2O5, Fe2O3 were found. Scanning electron microscopy(SEM) has shown one change of particle between 2μm at 90μm and apparent porosity, thermal analysis has shown loss of mass and residual decomposition in the TG, DTG and DTA curves.