Raw Coal Fly Ash Research Articles

Fly ash: An alternative to powdered activated carbon for the removal of eosin dye from aqueous solutions

This paper reports the use of powdered activated carbon (PAC) and raw coal fly ash (RFA) in the removal of eosin dye from aqueous solution in batch processes. Operational parameters such as contact time, initial dye concentration, pH and temperature were investigated. Adsorption equilibrium was established in 120 min for the two adsorbents. Langmuir and Freundlich isotherms were used to fit the adsorption data. Langmuir model gave the best fit in both cases. The adsorption capacities of PAC and RFA were found to be 62.28 mg/g and 43.48 mg/g, respectively. The highest percentage of eosin dye removal for both PAC (98%) and RFA (90%) was observed at pH 2. Pseudo first-order and pseudo second-order kinetic models were used to fit the adsorption data. Pseudo second-order kinetic model gave the best description of the adsorption of eosin dye onto the two adsorbents. Thermodynamic parameters, ΔH 0 , ΔS 0 and ΔG 0 confirmed the physical nature, spontaneity and the endothermic nature of the adsorption process. A regeneration technique and a process calculation for evaluating the adsorbent dose required were carried out. This study has shown that RFA is a good alternative adsorbent in the removal of eosin dye from aqueous solution.

Preparation of Alkali-Treaded Fly Ash Adsorbent and its Application for Cd<sup>2+</sup> Removal from Aqueous Solution

The modified fly ash (MFA) was prepared by calcining raw coal fly (FA) ash with Na2CO3 at high temperature. The preparation conditions of MFA and Effects of important parameters such as contact time, adsorbate concentration, pH and temperature on the sorption were researched, respectively. MFA obtained at calcining temperature of 550°C and FA/Na2CO3 mass ratio of 12 shows the effective removal for Cd2+ from aqueous solution, and the maximum removal was close to 100% with the adsorbent dosage of 10 g/L, initial Cd2+ concentration of 200 mg/L at 25°C. The adsorption kinetics of Cd2+ on MFA followed the pseudo-second-order model well and adsorption processes might be mainly controlled by intra-particle diffusion. The sorption is favourable at high temperature and the adsorption apparent activation energy was 68.08 kJ/mol which indicates the chemical nature of the adsorption.

Fly ash-based geopolymer for Pb removal from aqueous solution

The aim of this work was to synthesis highly amorphous geopolymer from waste coal fly ash, to be used as an adsorbent for lead Pb(II) removal from aqueous wastewater. The effect of various parameters including geopolymer dosage, initial concentration, contact time, pH and temperature on lead adsorption were investigated. The major components of the used ash in the current study were SiO 2, Al 2O 3 and Fe 2O 3 representing 91.53 wt% of its mass. It was found that the synthesized geopolymer has higher removal capacity for lead ions when compared with that of raw coal fly ash. The removal efficiency increases with increasing geopolymer dosage, contact time, temperature, and the decrease of Pb 2+ initial concentration. The optimum removal efficiency was obtained at pH 5. Adsorption isotherm study indicated that Langmuir isotherm model is the best fit for the experimental data than Freundlich model. It was found also that the adsorption process is endothermic and more favorable at higher temperatures.

Sewage sludge conditioning with coal fly ash modified by sulfuric acid

Activated sludge process to treat municipal and industrial wastewater produces huge amounts of excess sludge. Chemical condition has been employed widely to improve sludge mechanical dewatering, but the cost is high, thus it is very important to find cheap and effective conditioners. This paper studied the improvement of sludge dewaterability with coal fly ash modified by sulfuric acid (MCFA). Through orthogonal experiments with specific resistance to filtration (SRF) as the target index, acid concentration and soaking time were verified to be the important influencing parameters in coal fly ash modification. The optimal modification conditions were: acid concentration, 4 mol l −1; ratio of acid to coal fly ash, 5:1 ml g −1; soaking time, 3 h. After modification the specific surface area of coal fly ash increased from 2.810 to 3.376 m 2 g −1. The dewaterability and the settleability of the conditioned sludge were investigated with vacuum filtrating dewatering tests, centrifugal dewatering tests and settling experiments. The results showed that SRF of the sludge significantly decreased with coal fly ash addition, and the MCFA showed much stronger conditioning capacity than the raw coal fly ash (RCFA). Under a MCFA dosage of 273%, the SRF of the sludge decreased from 1.86 × 10 13 to 4.23 × 10 11 m kg −1, and the filter cake moisture decreased from 86.90% to 56.52%. The sludge conditioning mechanisms with MCFA mainly included improving floc formation through charge neutralization and adsorption bridging and providing the water transmitting passages by skeleton builder.

Adsorption of an acid dye onto coal fly ash

In this study, we found the raw coal fly ash (CFA) that had not been subjected to any pretreatment process had superior adsorbing ability for the anionic dye Acid Red 1 (AR1) than did two modified coal fly ashes (CFA-600 and CFA-NaOH). The adsorption capacities followed the order CFA > CFA-600 > CFA-NaOH, and they each increased upon increasing the temperature (60 °C > 45 °C > 30 °C). The adsorptions of AR1 onto CFA, CFA-600, and CFA-NaOH all followed pseudo-second-order kinetics. The isotherms for the adsorption of AR1 onto the raw and modified coal fly ashes fit the Langmuir isotherm quite well; the adsorption capacities of CFA, CFA-600, and CFA-NaOH for AR1 were 92.59–103.09, 32.79–52.63, and 12.66–25.12 mg g −1, respectively. According to the positive values of Δ H° and Δ S°, these adsorptions were endothermic processes. The ARE and EABS error function methods provided the best parameters for the Langmuir isotherms and pseudo-second-order equations, respectively, in the AR1–CFA adsorption system.

Radon exhalation of cementitious materials made with coal fly ash: Part 2 – testing hardened cement–fly ash pastes

Increased interest in measuring radionuclides and radon concentrations in fly ash (FA), cement and other components of building products is due to the concern about health hazards of naturally occurring radioactive materials (NORM). The paper focuses on studying the influence of FA on radon exhalation rate (radon flux) from cementitious materials. In the previous part of the paper the state of the art was presented, and the experiments for testing raw materials, Portland cement and coal fly ash, were described. Since the cement and FA have the most critical role in the radon release process relative to other concrete constituents (sand and gravel), and their contribution is dominant in the overall radium content of concrete, tests were carried out on cement paste specimens with different FA contents, 0–60% by weight of the binder (cement+FA). It is found that the dosage of FA in cement paste has a limited influence on radon exhalation rate, if the hardened material is relatively dense. The radon flux of cement–FA pastes is lower than that of pure cement paste: it is about ∼3 mBq m −2 s −1 for cement–FA pastes with FA content as high as 960 kg m −3.

Book review

Coal fly ash (CFA) is an industrial by-product generated during coal combustion process in power plants. Due to its chemical and mineralogical composition, CFA is considered as an abundant and cheap source of aluminosilicate to produce valuable advanced materials, such as zeolites, catalysts, photocatalyts, and geopolymers, with high adsorption capacity towards pollutants. In this review, the preparation methods and characterization of CFA-based adsorbents, as well as their application in removing aqueous pollutants, such as petroleum compounds, dyes, heavy metals, radioactive contaminants, COD and SS, and gaseous pollutants, such as carbon dioxide, sulfur dioxide, sulfuric acid, hydrogen sulfide, mercury, nitric oxide, benzene, toluene, and o- and p-xylene were summarized. The studies prove CFA-based adsorbents to be efficient and cost-effective alternatives to remove aqueous and gaseous pollutants. Recent investigations on the application of various surface modification techniques to improve the adsorption capacity of CFA-based adsorbents were also covered. The results indicate higher adsorption capacity of CFA-based adsorbents compared to raw CFA after surface modification.