The chemistry of cement and concrete

The retention of arsenate by four soils of Saskatchewan, Canada, and its relation to selected soil properties and anionic environments were studied. The data indicate that As retention by the soils at the dilute, As concentration range studied does not proceed through the precipitation of sparingly soluble arsenate compounds. Arsenate retention evidently proceeds through adsorption mechanisms. The adsorption maxima of the soils are not related to acidity and the contents of inorganic C, but are linearly related to amounts of ammonium oxalate-extractable Al and, to a lesser extent, to the contents of clay and ammonium oxalate-extractable Fe. Chloride, nitrate, and sulfate present at concentrations usually present in saline soils have little effect on the adsorption of As. Phosphate substantially suppresses As adsorption by the soils, and the extent of the suppression varies from soil to soil.

Adsorption of arsenate by soils and its relation to selected chemical properties and anions.

Fly ash (FA) generated as a waste produced from thermal power plants globally has started gaining as a potentially significant anthropogenic source of arsenic (As). In India electricity generation is predominantly dependent upon coal-based thermal power plants and are being producing huge amount of FA. Coal contains many toxic metals, arsenic is one of those, which is significantly toxic for aquatic and terrestrial life including human being. Coal used in Indian thermal power plants is mainly bituminous and sub-bituminous and which on combustion generate over 40% of FA. Generated FA is being disposed to open ash pond in thin slurry form. More than 65,000 acre of land in India is occupied for storage of this massively generated quantity of FA. Dumping of FA in open ash pond causes serious adverse environmental impacts owing to its elevated trace element contents, in particular the As which causes ecological problems. Although, the As problem in our country is not new, in recent years the occurrence of As contamination cases of agricultural soil, ground water as well as human health has resulted a great concern for its mitigation. Very recently India has been charged for being a “dumping hub for As”. Utilization of FA in India is still infancy (more than 38%) as compared to developed countries (more than 70%). In India FA is used particularly in cement production, brick industry, as road base, as amendments in the restoration ecology and forestry. This review emphasized on the concentration of As in FA, its fate and behaviour as hazardous element on human health, environment quality and on mitigation strategies to accomplish environmental management.

Arsenic hazards in coal fly ash and its fate in Indian scenario

Chemical absorption with aqueous amine solvents is the most advanced technology for postcombustion capture (PCC) of CO2 from coal-fired power stations and a number of pilot scale programs are evaluating novel solvents, optimizing energy efficiency, and validating engineering models. This review demonstrates that the development of commercial scale PCC also requires effective solvent management guidelines to ensure minimization of potential technical and environmental risks. Furthermore, the review reveals that while solvent degradation has been identified as a key source of solvent consumption in laboratory scale studies, it has not been validated at pilot scale. Yet this is crucial as solvent degradation products, such as organic acids, can increase corrosivity and reduce the CO2 absorption capacity of the solvent. It also highlights the need for the development of corrosion and solvent reclamation technologies, as well as strategies to minimize emissions of solvent and degradation products, such as ammo...

Towards commercial scale postcombustion capture of CO2 with monoethanolamine solvent: key considerations for solvent management and environmental impacts.

Soil Amendments and Environmental Quality

Abstract The generation of electricity by thermal conversion of coal results in significant volumes of solid waste. Most of these materials are disposed of in surface impoundments near coal-fired power plants or in active coal mines. Disposal rates vary from country to country. In the USA, 60–70 wt% of these materials are disposed. Although these materials rarely meet the definition of hazardous, leachate tests on some coal ash have shown them capable of producing elevated concentrations of some regulated metals. As a result of the well-documented environmental concerns posed by coal combustion, and the disposal of coal combustion products (CCPs), a large body of research has focused on characterizing the mechanisms of mobilization and attenuation of trace elements in coal and its ash. However, groups opposed to coal combustion or unregulated disposal of ash overlook the value of these materials as well-proven replacements for aggregate, cement, or soil in numerous engineering and agricultural applications. An extensive body of knowledge has been gathered describing the variability and versatility of these materials. It has been shown that proper utilization or management of ash requires a good understanding of its chemical, physical, and mineralogical properties. This chapter is intended to provide a broad overview of the chemistry and mineralogy of coal, and the combustion products that are formed when coal is burned.

The chemistry and mineralogy of coal and coal combustion products

Leachate derived from unlined coal ash disposal facilities is one of the most significant anthropogenic sources of selenium to the environment. To establish a practical framework for predicting transport of selenium in ash leachate, sorption of Se(IV) and Se(VI) from 1 mM CaSO{sub 4} was measured for 18 soils obtained down-gradient from three ash landfill sites and evaluated with respect to several soil properties. Furthermore, soil attenuation from lab-generated ash leachate and the effect of Ca{sup 2+} and SO{sub 4}{sup 2-} concentrations as well as pH on both Se(IV) and Se(VI) was quantified for a subset of soils. For both Se(IV) and Se(VI), pH combined with either percentage clay or dithionite-citrate-bicarbonate (DCB)-extractable Fe described {gt} 80% of the differences in sorption across all soils, yielding an easy approach for making initial predictions regarding site-specific selenium transport to sensitive water bodies. Se(IV) consistently exhibited an order of magnitude greater sorption than Se(VI). Selenium sorption was highest at lower pH values, with Se(IV) sorption decreasing at pH values above 6, whereas Se(VI) decreased over the entire pH range (2.5-10). Using these pH adsorption envelopes, the likely effect of ash leachate-induced changes in soil pore water pH with time on selenium attenuation bymore » down gradient soils can be predicted. Selenium sorption increased with increasing Ca{sup 2+} concentrations while SO{sub 4}2- suppressed sorption well above enhancements by Ca{sup 2+}. Soil attenuation of selenium from ash leachates agreed well with sorption measured from 1 mM CaSO{sub 4}, indicating that 1 mM CaSO{sub 4} is a reasonable synthetic leachate for assessing selenium behavior at ash landfill sites.« less

Selenium(IV) and (VI) Sorption by Soils Surrounding Fly Ash Management Facilities

Characterizing As(III,V) adsorption by soils surrounding ash disposal facilities

This article presents a study on the processing of waste dust from electrical smelting of ilmenite concentrates with the removal of silica from them by alkaline and fluoride methods. The study of the smelting dust leaching by caustic soda solutions included investigation of the effect of sodium hydroxide concentration, process time, temperature, S:L ratio. The optimum conditions of concentrate electric smelting dust leaching - temperature 80-90 °С, duration 90-120 minutes, S:L ratio = 1:5, sodium hydroxide solution concentration 110-115 g/dm3 were determined. The optimum conditions for fluorination of electric melting dust were determined, at which the sublimation degree of silicon fluoride was 84.2 %. Studies have been performed to decomposite obtained silicon-containing sublime in the presence of ammonia agent. The optimum pyrolysis modes that provide the separation of fluoride and silicon oxide - temperature 530-560 °C and duration of 60-80 min have been determined based on the results of thermal analysis and studies on the process duration effect. The silicon oxide content in the obtained product was 96.3%.

Methods of silica removal from pyrometallurgical processing wastes of ilmenite concentrate

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Papers

The chemistry and mineralogy of coal and coal combustion products

Selenium(IV) and (VI) Sorption by Soils Surrounding Fly Ash Management Facilities

Characterizing As(III,V) adsorption by soils surrounding ash disposal facilities

Methods of silica removal from pyrometallurgical processing wastes of ilmenite concentrate