Natural zeolite is believed to be able to effectively reduce heavy metal levels in water. However, due to the weakness of natural zeolites which have a low surface area and impurity so that the adsorption ability of heavy metals becomes less optimal. Increasing the surface area by using high energy milling is expected to optimize the ability of adsorption. In this study, the particle size of natural zeolite was reduced by using high energy milling then activated with HCl and NH4Cl. The adsorption process was carried out by mixing activated zeolite and activated zeolite milling(activated zeolite fine powder) in a solution of metal ions Zn(II) and Cd(II). SEM-EDX analysis showed a change in surface morphology size on activated zeolite milling and GSA indicated an increase in surface area from 69.48 m2/g to 97.9 m2/g. Activated zeolite tends to having a little bigger in ability of adsorption to Cd(II) ions and Zn (II) ions than activated zeolite milling in highest variation of concentration, 800 ppm. In optimum contact time of adsorption, activated zeolite could adsorp Cd(II) ions shorter nevertheless longer to Zn(II) ions than activated zeolite milling. Both of the zeolites have ability to adsorp Zn(II) ions more than Cd(II) ions.

A large amount of sludge is produced by the geothermal brine at the Dieng Geothermal power plant, exceeding 165 tons per month. This sludge is generally not utilized, except for use in landfills. The precipitate (sludge) is primarily composed of silica. The aim of this research is to synthesis mesoporous silica (SiO2) xerogel from geothermal sludge (GS) and to investigate the effects of pH as an effort to elevate the economic value of sludge through alkaline extraction followed by acidification. SiO2 xerogel was prepared by extracting the GS to become sodium silicate (Na2SiO3) assisted by a base NaOH and precipitated using H2SO4 as a gelation agent. The FTIR analysis of the SiO2 xerogel showed a group of silanol (Si-OH) and siloxane (Si-O-Si). The XRD analysis indicated that SiO2 xerogel was amorphous. Furthermore, it was observed from nitrogen absorption-desorption using BET (Breneur-Emmet-Teller) method test that decreased pH tends to the specific surface area increase, and the pore size becomes decrease. The largest specific surface area observed at SiO2 xerogel prepared at pH of 5.5 reached 400.10 m 2 /g with a pore size of 4.5 nm. The pore sized for all cases was in the range of 4 ~12 nm, indicating that the SiO2 xerogels were mesoporous. Pore size of the as-prepared silica affected the thermal stability property of the sample.