COAL FLY ASH-BASED GEOPOLYMER AS ADSORBENT FOR Cu (II) and Zn (II) IONS

• Main Author: DARMAYANTI (NIM: 35314003), LITA
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/28626
• Institution: Institut Teknologi Bandung

The use of coal as an alternative source of energy produces waste in the form of very large amounts of fly ash and can endanger health and the environment if not managed properly. Fly ash has the potential to be used as an adsorbent to replace activated carbon or zeolite. Fly ash generally has a low adsorption capacity so it needs to be activated first. One of the activation techniques is with geopolymerization. Geopolymers are aluminosilicate inorganic polymers synthesized from natural materials (kaolin) or industrial waste (coal fly ash, blast furnace slag) with strong alkaline solutions. The main structure of the geopolymer consists of tetrahedral bonds of Si-O-Si and Si-O-Al by dividing the O atoms evenly to form an amorphous aluminosilicate framework. The presence of negatively charged Al in this framework requires positively charged ions to balance it. The cation types commonly used for geopolymer synthesis are Na and K. Geopolymers as adsorbent materials have many advantages such as higher adsorption capacity than natural zeolites and some other adsorbent materials, processes making is simpler, and does not require high temperatures. Geopolymer can be synthesized at a temperature of <100C. The materials used are cheap and easy to obtain. <br /> <br /> <br /> <br /> <br /> <br /> <br /> Although geopolymers have been widely researched, but its applications for processing wastewater is relatively rare. This study aims to intrensively examine the geopolymerization process that can increase the adsorption capacity of fly ash on heavy metals and to study the adsorption mechanism on Cu and Zn ions. The end product of geopolymer is very much determined by characteristic of raw materials, condition of synthesis, types of cations and alkaline solution concentrations, as well as curing conditions such as time and temperature. <br /> <br /> <br /> <br /> <br /> <br /> <br /> The research began by characterizing coal fly ash originating from the textile industry. Characterizations include XRF, XRD, FTIR, SEM, and N2 adsorption-desorption test. Then, adsorption test of coal ash fly on Cu metal was carried out. The results showed the adsorption of Cu in coal fly ash was influenced by pH, adsorbent dose, contact time, and initial concentration of Cu metal. The adsorption process follows the Langmuir model and second-order pseudo kinetics models. Coal fly ash adsorption capacity is 5.09 mg/g. <br /> <br /> <br /> <br /> <br /> <br /> <br /> Geopolymer synthesis was carried out in stages. The first stage aims to determine the type of alkali and water/solid ratio which can produce geopolymers with large adsorption capacity. The alkali types used were NaOH, KOH, NaOH+Na2SiO3, and KOH+Na2SiO3 and the water/solid ratio was 0.6; 0.8 and 1.0. The test results showed that the geopolymer synthesized with NaOH+Na2SiO3 with a water/solid ratio of 0.6 has the greatest adsorption capacity. The synthesis was continued with this activator to determine the alkali concentration expressed in the Na2O/SiO2 ratio and the treatment time. The ratio of Na2O/SiO2 used is 0.16; 0.3, and 0.5 with treatment times 1, 3 and 5 days. The increase in the ratio of Na2O/SiO2 is achieved by increasing the amount of NaOH and decreasing Na2SiO3 in the activator solution. The increase of NaOH and decrease of Na2SiO3 reached the optimum limit at a ratio of Na2O/SiO2 0.3. Geopolymer (Gr3t5) synthesized with a ratio of Na2O/SiO2 0.3 and a treatment time of 5 days produced geopolymers with the largest adsorption capacity. <br /> <br /> <br /> <br /> <br /> <br /> <br /> The geopolymerization product is semi-crystalline amorphous aluminosilicate gel and unreacted residual material. To study the structural changes that occur in geopolymers, characterization is carried out as is on fly ash. The adsorption process occurs in both crystalline and amorphous phases. Geopolymer adsorption ability is strongly influenced by the crystalline phase fraction, the T-O bond fractions (whether bridging or terminal) in aluminosilicate gel, Si/Al ratio, pore volume, and surface area. <br /> <br /> <br /> <br /> <br /> <br /> <br /> The adsorption study was carried out on selected geopolymers (Gr3t5). The results showed the adsorption process of Cu and Zn ions fitted well with Freundlich isotherms. The value of the adsorption linearity constant, n ranges from 1-10 which shows an effective adsorption process and a large KF value indicates that the geopolymer has a high affinity for Cu and Zn ions. The monolayer adsorption capacity is 81.30 mg/g for Cu ions and 64.01 mg/g for Zn ions.In a solution containing a mixture of Cu and Zn, competitive adsorption is antagonistic. There is competition between of two metals in occupying the active site on the surface of the adsorbent so that the adsorption capacity decreases. The kinetic followed pseudo-second-order kinetics indicating chemisorption to be the mechanism of adsorption. Weber Morris’s intraparticle diffusion models showed that two different stages for removal of the metals. Thermodynamic parameters were evaluated and it was found that the adsorption was spontaneous and endothermic in nature. Mechanism of adsorption is physisorption and chemisorption that was driven with electrostatic attractions, ion exchange, hydrogen bonds, and coordination covalent <br />