Method for Recovering Gold, Silver, Copper and Iron from Plasma-Caused Slag Containing Valuable Metals

Abstract

There is disclosed an environmentally friendly method for recovering gold, silver, copper and iron from valuable metal-contained plasma-molten slag. At first, plasma is used to burn the used printed circuit boards, thus producing the slag. Then, the slag is grinded. Then, leaching, crystallization, precipitation, replacement and electric winning are conducted to recover gold, silver, copper and iron.

1 . A method for recovering valuable metals from used printed circuit boards comprising the steps of:
 providing plasma for burning the used printed circuit boards, thus providing slag;   grinding the slag;   providing a sieve with meshes of 0.149 mm for sieving the slag, thus separating large debris larger than 0.149 mm from small debris smaller than 0.149 mm;   providing a magnet for testing the large debris, thus separating ferromagnetic large debris from non-ferromagnetic large debris so that the ferromagnetic large debris can be provided to a steel-making factory while the non-ferromagnetic large debris, which is rich in copper, can be provided to a copper refinery;   providing a magnet to test the small debris, thus separating ferromagnetic small debris from non-ferromagnetic small debris so that the ferromagnetic small debris can be provided to a steel-making factory;   providing 18N sulfuric acid for leaching the non-ferromagnetic small debris, wherein the solid/liquid ratio is retained at 10 g/50 ml, and the temperature is kept at 70 degrees Celsius so that 90.56% of the copper is released from the non-ferromagnetic small debris to the sulfuric acid after 1 hour, thus separating primary copper-contained leaching solution from primary sulfuric acid-leached residue;   retaining the copper-containing leaching solution at 27 degrees Celsius for 48 hours for crystallization so that 58.28% of the copper is recovered in the form of copper sulfate crystals, thus separating the copper sulfate crystals from optimal crystallization filtrate;   replacing the copper in the optimal crystallization filtrate with iron powder used as replacement reagent so that 100% of the copper is recovered from the optical crystallization filtrate when the amount of the iron reaches 100 times of the theoretical value, thus providing copper powder;   providing 18N sulfuric acid for leaching the sulfuric acid-leached residue again, wherein the solid/liquid ratio is retained at 50 g/50 ml, and the temperature is kept at 70 degrees Celsius so that 100% of the copper is released from the sulfuric acid-leached residue to the sulfuric acid after 2 hours, thus separating secondary copper-containing leaching solution from secondary sulfuric acid-leached residue;   replacing the copper in the secondary copper-contained leaching solution with iron powder used as replacement reagent so that 100% of the copper is recovered from the secondary copper-contained leaching solution when the amount of the iron reaches 150 times of the theoretical value, thus providing copper powder;   providing 8N nitric acid for leaching the sulfuric acid-leached residue, wherein the solid/liquid ratio is retained at 1 g/50 ml, and the temperature is kept at 70 degrees Celsius so that 100% of the silver is released to the nitric acid from the sulfuric acid-leached residue after 4 hours, thus separating optimal silver-containing leaching solution from nitric acid-leached residue;   providing ammonia solution for adjusting the pH of the optimal silver-contained leaching solution;   providing 12N hydrochloric acid for precipitation, wherein the ratio of the hydrochloric acid to the silver-contained leaching solution is 1:4 so that 100% of the silver is recovered in the form of silver chloride;   providing 100% aqua liquid for leaching the nitric acid-leached residue, wherein the ratio of the nitric acid-leached residue to the 100% aqua liquid is 0.5 g/50 ml, and the temperature is 70 degrees Celsius so that 100% of the gold is released to the aqua liquid from the nitric acid-leached residue after 4 hours, thus providing optimal gold-contained leaching solution; and   replacing the gold in the optimal gold-contained leaching solution with zinc powder used as replacement agent, thus recovering 99.43% of the gold from the optimal gold-contained leaching solution.