Method of pretreatment and bromine recovery of PCB incineration ash

A method of pretreatment and bromine recovery of printed circuit board incineration ash, comprising the steps of:

• (1) alkali leaching, further comprising the steps of:
• treating the printed circuit board incineration ash with an alkali leaching solution for 1 to 2 hours, wherein the alkali leaching solution is made of a mixture of sodium hydroxide and ammonia, wherein the concentration of sodium hydroxide is 5˜20% by mass, and the concentration of ammonia is 5˜20% by mass, the solid-liquid ratio of ash to the leaching solution is 1:5˜1:10 Kg/L, the leaching temperature is 35˜55° C., meanwhile keep blowing air with agitation, wherein blast air volume per cubic meter of the leaching solution is 0.01˜0.1 m3/min;
• stopping blowing the air and continuing agitating, adding 1˜3 g copper powder into every liter of the leaching solution;
• carrying out the reaction for 10˜30 minutes;
• and
• performing filtration to obtain a mixed alkali leaching slag and a mixed alkali leaching solution;
• (2) copper extraction back-extraction, further comprising the steps of:
• extracting copper from the mixed alkali leaching solution from step (1) with Benzaldehyde,2-hydroxy-5-nonyl-,oxime, and
• performing back-extraction with a sulfuric acid solution to obtain copper sulfate and raffinate;
• (3) neutralization-precipitation, further comprising the steps of:
• adding a sulfuric acid to the raffinate in step (2) for neutralization and precipitation, to obtain a precipitated slag and a precipitated solution;
• (4) bromine evaporative crystallization, further comprising the steps of:
• performing bromine evaporative crystallization for the precipitated solution in step (3), to obtain bromine salts and crystal mother liquor;
• (5) regeneration, further comprising the steps of:
• regenerating the crystal mother liquor in step (4) by adding lime, to obtain gypsum and post-regeneration solution;
• (6) acid pickling, further comprising the steps of:
• performing acid wash of the precipitated slag in step (3) with sulfuric acid to obtain lead sulfate and acid pickling solution;
• (7) zinc evaporative crystallization, further comprising the steps of:
• performing evaporative crystallization of the acid pickling solution in step (6), to obtain zinc sulfate and crystallized solution, wherein the crystallized solution is returned to the acid pickling process as part of the acid washing solution;
• and
• (8) zinc and copper removal, further comprising the steps of:
• removing zinc and copper from the mixed alkali leaching slag in step (1), by contacting the mixed alkali leaching slag with a leaching solution of 100˜200 g/L sulfuric acid solution, the leaching temperature being 55˜75° C. and the leaching time being 1˜3 hours, and hydrogen peroxide being added during leaching, wherein the mass of hydrogen peroxide added to per liter of the leaching solution is 40˜80 g/L;
• performing a filtration to obtain copper/zinc removal residual and copper/zinc removal filtrate;
• and
• separating the copper and the zinc from the copper/zinc removal filtrate to obtain copper sulfate and zinc sulfate, wherein the copper/zinc removal residual is used for enrichment of precious metals and recovery of valuable metals.