NOVELTY - Potassium feldspar raw material is crushed to 100-200 mesh, and provided into a mixer. Caustic sludge is added to the mixer, mixed, the mixed material is provided into a reaction furnace, and calcined, to obtain gas mixture. The gas mixture is filtered, and washed. The resultant product is fed into a leaching vessel containing leaching solution, heated, stirred, provided into plate-frame filter press, press-filtered, separated, and resultant product is further processed, to obtain aluminum hydroxide and ammonium sulfate. Thus processing of caustic sludge is carried out.    USE - Method for processing caustic sludge (claimed).    ADVANTAGE - The method enables easy, economical and simple processing of caustic sludge with suppressed environmental pollution caused by caustic sludge pile.    DETAILED DESCRIPTION - Potassium feldspar raw material is weighed, crushed to 100-200 mesh, and provided into a mixer by a raw material conveying system. Caustic sludge is added to the mixer, mixed, the mixed material is provided into a reaction furnace, and calcined, to obtain gas mixture. The gas mixture is filtered by multi-stage filtration recycling system, washed, and dust is discharged. The resultant product is fed into a leaching vessel containing leaching solution, heated, heat-preserved, stirred, provided into plate-frame filter press, press-filtered, and filtrate (a1) and filter residue (a2) are separated. The obtained filtrate (a1) is provided into an evaporator, and evaporated to collect product containing sodium chloride, potassium chloride and calcium chloride. The filter residue (a2) is washed, filtered, acidified in which metal ion is ionized, press-filtered, and filtrate (b1) and filter residue (b2) are separated. The filter residue (b2) is washed, dissolved in alkali solution in a reactor, subjected to alkaline treatment, press-filtered, and filtrate (c1) and insoluble residue (c2) are separated. The filtrate (c1) is sodium silicate mother liquor used for production of sodium metasilicate pentahydrate or white carbon black. The insoluble residue (c2) is used as cement clinker. The filtrate (b1) is acidified to ionize metal cation, press-filtered, and separated, to obtain ferric hydroxide and filtrate (d1). The filtrate (d1) is acidified, press-filtered, and separated, to obtain aluminum hydroxide and ammonium sulfate. Thus processing of caustic sludge is carried out. The weight ratio of potassium feldspar raw material and caustic sludge is 0.5-3:1.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart illustrating the base slag process. (Drawing includes non-English language text)