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The synthesis of matrix silica-potassium-humic acid gel (Si-K-HA s ) has been performed successfully by gradual extraction and acidification method. The extraction was carried out in two stages: 1) extraction of humic substances from peat prepared by potassium hydroxide to produce potassium humate (K-HA S ) solution , 2) extract ion silica from geothermal sludge using K-HAs solution to produce Si-K-HAs solution. Acidification of Si-K-HAs solution prepared by citric acid (1-3N) to produce matrix gel of Si-K-HAs. The Si- K-HAs matrix gel products are characterized by Fourier Transform InfraRed ( FTIR ) , X-ray fluroscence ( XRF ) , and Brunauer–Emmett–Teller ( BET ) analysis . The acidification process was carried out in neutral to acid (pH 3-7) conditions and the results showed that at neutral pH no Si-K-HAs gel formed. IR spectra confirm ed the presence of humic acid in the gel product, whereas XRF analysis confirm ed the presence of potassium (K) and silica (SiO 2 ) in the gel product. The molar ratio of SiO 2 :K 2 O in the product is 0.9 - 0.3 in the pH range of 3- 5 . Si-K-HA s powder can be used as soil fertilizer especially for soils that lack silica, humic, and potassium nutrients or for future application development . Keywords: gradual extraction; geothermal sludge; matrix gel; humic substance

Synthesis of Matrix Si-K-HAs Gel from Geothermal Sludge and Peat