Wahyu Prasetyo Utomo

Preparation of La 0.7 Sr 0.3 Co 0.2 Fe 0.8 O 3-δ (LSCF 7328) by Combination of Mechanochemical and Solid State Reaction

Structure evolution and morphology of La0.7Sr0.3Co0.8Fe0.2O3-δ (LSCF 7328) were investigated during two different preparation methods namely mechanochemical and combination of mechanochemical-solid state. The result shows that no characteristic peak of perovskite oxide was found on the diffractogram of the product of sole mechanochemical method at 600 rpm and up to 12 h of high energy milling process. On the other hand, the manual grinding method that was followed by solid state calcination produces irregular particle size. Due to the result, the combination of both methods was proposed to obtain the fine structure formation and particle size distribution. Rietveld refinement was used to investigate the lattice distortion. It was found that unit cell remains unchanged at increasing milling time. Moreover, the combination method produces regular particle size at milling time of 0.5 h. At longer milling time, the more regular particle size is formed which comes from highly energy transfer of milling.

Cd2+ and Cr3+ Cation Immobilization by Using Geopolymer Based on PT. IPMOMI Fly Ash

This study investigates the immobilization of Cd2+ and Cr3+ by using geopolymer paste based on PT. IPMOMI fly ash. The best composition of geopolimers paste was determined based on the highest magnitude of its 7 days compressive strength. Geopolymer pastes were prepared by varying SiO2/Al2O3 and Na2O/SiO2 molar ratio of the starting materials. X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) were employed to examined these compositions. The molar ratio of SiO2/Al2O3 6.46 was found to produce the highest compressive strength of the resulting geopolymer paste, i.e 25 MPa and increased to 33.17 MPa by adjusting the ratio of Na2O/SiO2 to 0.65. Cd2+ and Cr3+ cations were added into geopolymers resin at the level of 1000 – 16000 ppm (mg/kg fly ash) and it was found to improve their compressive strength. The addition of 4000 ppm of Cd2+ increased the compressive strength to 38.6 MPa while the inclusion of 6800 ppm of Cr3+ reached 47.83 MPa. Further addition of cations reduced these values and the lowest compressive strength was observed on the addition of 16000 ppm of Cd2+ and Cr3+, i.e 8.65 MPa and 4.39 MPa, respectively. Leaching test was conducted by using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and the distribution of heavy metal cations were examined by using SEM-EDX. The results showed that geopolymer pastes were able to immobilize Cr3+ at the studied level as there was no trace of Cr3+ detected after 6.5 hours of leaching. Geopolymer pastes were also found to completely immobilize Cd2+ at the level of 1000 ppm albeit the addition of 16000 ppm results in 6.26% leached out of this cation.