Physico-Chemical Characterization and Leaching of Desulphurization Coal Fly Ash

Abstract

Fly ash produced by coal combustion using two types of desulphurization process were studied: a conventional pulverized coal boiler equipped with lime injection (PCL ash), and a circulating fluidized bed combustion boiler with limestone injection (CFBC ash). The ashes were characterized completely: granulometry, morphology, mineralogy, chemical composition and behaviour to water contact. Both PCL ash and CFBC ash present similar features: fine granulometry, presence of anhydrite phase and sulphate content. However, PCL ash also shows lots of spherical particles, unlike CFBC ash, and a much higher lime content, due to the lower desulphurization rate in PC boilers. Unlike CFBC ash, most of the trace elements in PCL ash show an inverse concentration-particle size dependence. Leachates obtained from both samples are rich in soluble salts [CaSO4 and Ca(OH) 2] and arsenic and selenium are prevented from solubilizing by high lime content. In wetted PCL ash, the formation of ettringite crystals stabilizes calcium and sulphate ions. Simultaneously, arsenate, selenate and chromate anions are trapped in the crystal. CFBC ash does not really harden because the lime content is too low. However, the leached selenium concentration is cut down in wetted CFBC ash samples. © 1996 ISWA

The physical and chemical performance of artificial reef blocks made using quarry by-products

“…This concurs with Hower et al (1996), who reported that arsenic concentrations in the base material and subsequent levels of leaching are not directly related. A more important factor may be that trace metals such as arsenic, molybdenum, and vanadium are bound through chemical reactions occurring during the hardening of concrete (Lecuyer et al, 1996). This binding process may also account for the lower leaching of uranium from concrete compared with granite even though uranium was present in approximately equal concentrations in both base materials.…”

Effects of circulating fluidized bed combustion (CFBC) fly ashes as filler on the performances of asphalt

“…[6,7] However, the resultant CFBC fly ashes (CFAs) distinctly differ from the conventional pulverized coal combustion fly ashes (PFAs) in physical and chemical characteristics. [8,9] While the majority of PFAs could be utilized in construction materials such as cement and concrete, [9,10] the disposal of the increasing amount of CFAs still poses challenges such as highly exothermic behavior on wetting, highpH leachate, and excessive expansion in landfill, etc. [11] Generally, CFAs do not conform to either North American standards nor European ones as components or additives to concretes.…”

Analysis of the Distribution of Chemical Compounds from Fly Ash Exposed to Weather Conditions

“…Chemicals which partake in leaching are also waste heavy metals condensed on fly ahs particles, which change into a gaseous state during combustion, and as a result of precipitation on dry waste dumps and due to the contact with process water on wet waste dumps, they are washed off from the surface of the particles and penetrate into the soil and ground water, and then to living organisms. If the deposited waste has an alkaline reaction, then the main environmental hazard will be posed by liberating sodium, potassium and calcium sulphates (Lecuyer et al, 1996). A particular danger is caused by acid precipitation which, due to its aggressiveness, promotes the solubility of those compounds.…”