NOVELTY - Comprehensive recycling of leached slag in electrolytic manganese metal and manganese dioxide production comprises: recycling heavy and noble metals in leached slag; recycling manganese and iron by magnetic separation method; treating the tailing ore slurry by e.g. hydrolyzing sulfuric acid and plant carbohydrates, reacting with tailing ore slurry and generating soluble sulfates of trace heavy metals; preparing a complex organic fertilizer; separating the trace heavy metals in the complex organic fertilizer; recycling alkaline earth metals; and crystallizing and separating ammonium sulfate.    USE - The method is useful for comprehensive recycling of leached slag in electrolytic manganese metal and manganese dioxide production.    ADVANTAGE - The method can recycle ferromanganese ore concentrate to obtain heavy metals (cobalt, nickel, copper, silver and tin), noble metal concentrate, quartz sand, ammonium sulfate, and complex fertilizer base material containing nitrogen, phosphorus, potassium, humic acid, and required amount of trace elements, and hence ensures zero discharge during electrolytic manganese metal and manganese dioxide production.    DETAILED DESCRIPTION - Comprehensive recycling of leached slag in electrolytic manganese metal and manganese dioxide production comprises: (i) recycling heavy metals and noble metals; (ii) recycling manganese and iron; (iii) treating the tailing ore slurry and preparing a complex organic fertilizer; (iv) separating the trace heavy metals in the complex organic fertilizer; (v) recycling alkaline earth metals; and (vi) crystallizing and separating ammonium sulfate. The recycling of heavy and noble metals comprise recycling cobalt, nickel, copper, silver and tin of leached slag in electrolytic manganese metal and manganese dioxide production. The recycling of manganese and iron in the leached slag is carried out by magnetic separation method. The tailings slurry processing and complex organic fertilizer preparation comprises performing hydrolysis reaction of sulfuric acid (70-90 wt.%) and plant carbohydrates, stirring and mixing with the tailing ore slurry, reacting, generating soluble sulfates of trace heavy metals in tail ore slurry, passing the filtrate to a heavy metal sulfide precipitation reactor, performing natural fermentation of plant carbohydrate to obtain the organic complex fertilizer, where the plant carbohydrate is plant straw, rice husk, molasses of sugar factory and paper pulp waste liquid. The separation of trace heavy metals in the complex organic fertilizer comprises collecting the filtrate after the reaction, adding a vulcanizing agent, and stirring to precipitate the heavy metal sulfide, where the vulcanizing agent is sodium sulfide, ammonium sulfide or sodium dimethyldithiocarbamate, and its adding amount is based on the trace heavy metal content. The recycling of alkaline earth metals comprises collecting water from the metal sulfide precipitation tank, adding into a carbonization reactor added with a carbonization agent, uniformly stirring to ensure complete reaction, and passing the solution to a carbonization precipitation tank to precipitate the alkaline-earth metal carbonate, where the carbonizing agent is sodium carbonate, potassium carbonate, ammonium bicarbonate or ammonium carbonate. The crystallization and separation of ammonium sulfate crystals comprises separating ammonium sulfate crystals from the aqueous solution discharged from the carbonization precipitation tank, crystallizing ammonium sulfate by starting a multi-effect evaporation crystallizer if the concentration of ammonium sulfate is more than 180 g/l and continuously conveying the evaporative cooling water into a high water level pond for producing recycled water, or directly conveying the aqueous solution into the high water level pond for producing recycled water if the concentration of ammonium sulfate is not greater than 180 g/l.