Ahmer Ali Siyal

A Review on Geopolymers as Emerging Materials for the Adsorption of Heavy Metals and Dyes

The world water resources are contaminated due to discharge of a large number of pollutants from industrial and domestic sources. A variety of a single and multiple units of physical, chemical, and biological processes are employed for pollutants removal from wastewater. Adsorption is the most widely utilized process due to high efficiency, simple procedure and cost effectiveness. This paper reviews the research work carried out on the use of geopolymer materials for the adsorption of heavy metals and dyes. Geopolymers possess good surface properties, heterogeneous microstructure and amorphous structure. The performance of geopolymers in the removal of heavy metals and dyes is reported comparable to other materials. The pseudo-second order kinetics and Langmuir isotherm models mostly fit to the adsorption data suggesting homogeneous distribution of adsorption sites with the formation of monolayer adsorbate on the surface of geopolymers. Adsorption of heavy metals and dyes onto geopolymers is spontaneous, endothermic and entropy driven process. Future research should focus on the enhancement of geopolymer performance, testing on pollutants other than heavy metals and dyes, and verification on real wastewater in continuous operation.

Determination of anisotropy and multimorphology in fly ash based geopolymers

In this study, Malaysian coal fly ash-based geopolymers were investigated for its morphology and chemical composition using scanning electron microscopy coupled with energy dispersive X-rays (SEM-EDX). Geopolymer was synthesized using sodium hydroxide as activator. SEM studies revealed multiphasous structure of the material, composed of geopolymeric gel, partially reacted fly ashparticles and selectively leached particles. EDX analysis confirmed the chemical composition of different regions. Infra red spectroscopic studies supported the SEM-EDX analysis by confirming presence of unreacted quartzite and mullite in geopolymers. It is concluded that geopolymers possese a non uniform chemistry through out the structure.

Quantification of geopolymers production by chemical methods- A short review

Inorganic polymers are the aluminosilicate materials possessing properties superior than ordinary Portland cement. In this review paper the chemical techniques used for determining degree of reaction of fly ash or the quantity of geopolymer material produced have been discussed. These methods determine the amount of product formed in percentages. The methods include HCl method, salicylic acid method, and picric acid method. These methods are not only used for fly ash but they are being used for determining the degree of reactions of metakaolin and other pozzolanic materials. The picric acid is an explosive material and its transportation in high concentration is dangerous. During its use in laboratory there is also the risk of fire associated with it. According to the microscopic analysis results the picric acid attack dissolves small amount of fine unreacted fly ash particles also. The salicylic acid is easily available but the residue from its treatment contains unreacted fly ash particles, hydration ph...

Kinetics of Geopolymer Solidification Study Using Texture Analyzer

The aim of this work was to study on the solidification kinetics of geopolymer using the Avrami Kinetics Theory by varying types of alkali solution and alkali concentration at different temperatures. Tests were carried out using Leatherhead Food Research Association (LFRA) Texture Analyzer to analyze the solidification profile. The results indicated that potassium hydroxide at low concentration had better performance in achieving faster time for geopolymerization process. Higher temperatures of 35°C used in the solidifying process of the geopolymer reduced the setting time. Based on the kinetic study, the growth rate (K) increased with the concentration of alkali activator and temperature. The Avrami exponent (n) trend was increased as growth rate increased. From the values of Avrami exponent obtained it could be suggested that the geopolymer had one, two or three dimension growth forms depending on the parameters selected.

Experimental Study of Geopolymer Solidification Kinetics

Geopolymers are formed from silica and alumina oxides mixed with alkali hydroxide or alkali silicate. This paper presents the findings on the study of the solidification of fly ash geopolymer through setting time by varying alkaline activators, their concentrations and geopolymer curing temperature. This work focuses on the transformation of geopolymer from liquid paste to solid through Avrami’s Kinetic Theory. From the experimental results, alkaline activation with sodium silicate produced shortest time for geopolymer solidification as compared to KOH and NaOH. The increase in concentrations of alkaline solution and curing temperatures were found to reduce setting time for geopolymer’s solidification. From Avrami theory perspective, the growth forms of geopolymer in the geopolymerization process exhibit two and three dimensional structure with the presence of secondary nucleation.

Effect of NaOH and Water Contents on Solidification of Sodium Silicate Free Geopolymer

Geopolymers are fast setting binder materials possessing strength comparable with Portland cement. In this study solidification and bonding behavior of sodium hydroxide activated class F fly ash geopolymers were determined. Solidification was determined using Vicat apparatus and bonding behavior study was carried out using Fourier transform infrared spectroscopy (FTIR). The decrease in solidification time from 105 minutes to 90 minutes was observed when Na/Al ratio increased from 1 to 1.4. By changing liquid to solid (L/S) ratio from 0.154 to 0.231 initial and final setting times found to increase. FTIR results showed main peaks at 1000 cm-1 and 1432 cm-1 due to asymmetric stretching of Al-O/ Si-O bonds.