Determination of the optimum combination of alkali activator/fly ash ratio and Na‚‚SiO‚ƒ/NaOH ratio for thesolidification/stabilization of chromium-contaminated soil using fly ash-based geopolymer

• Main Authors: Castillo, Calvin T., Hernandez, Gelvin T.C., Pua, Alyssa Alexis Y.
• Format: text
• Language: English
• Published: Animo Repository 2015
• Subjects: Alkali-aggregate reactions; Chemical reactions
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/5876
• Institution: De La Salle University

Hexavalent chromium [Cr(VI)] poses a serious health concern due of its carcinogenic and teratogenic effects. Moreover, Cr(VI) is difficult to immobilize thus becoming a potential soil contaminant. One such method for soil treatment is through solidification/stabilization (S/S) technology. Using Fly ash, a by-product generated by the combustion of coal for energy production by power plants which is either recycled or thrown in landfills. Due to its pozzolanic properties, it can be used as an alternative binder in S/S technology and recently, it has shown potential in heavy metal immobilization. This study investigated the alkali activator/fly ash (AA/FA) mass ratio and the activator solution Na2SiO3/NaOH mass ratio that will minimize leachability and maximize compressive strength. The AA/FA ratio was varied from 0.2 to 0.4 while the Na2SiO3/NaOH ratio was varied from 1 to 2.5, both in mass basis. On the other hand, soil/FA ratio was constant at 1.0. Using the Central Composite Design (CCD), nine different mix proportions were generated from the ratios at two levels each. Compressive strength and leachability were tested as responses. The geopolymers formed yielded compressive strengths ranging from 118 to 302 kPa. A regression model was made and by using the desirability function, an optimum compressive strength of 280 kPa was achieved at an AA/FA ratio 0.4 and at a Na2SiO3/NaOH ratio of 2.27. The results showed that the simultaneous increase in Na2SiO3/NaOH ratio with AA/FA ratio yielded an increase in compressive strength at high AA/FA ratios. As for the leachability of Cr(VI), all samples were successful in solidifying/stabilizing the contaminated soil and were below the regulatory limit of 5mg/L set by the US EPA.