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.

Description

FIELD OF THE INVENTION

The present invention relates to an environmentally friendly method for recovering gold, silver, copper and iron from valuable metal contained plasma-molten slag via plasma burning, grinding, leaching, crystallization, precipitation, replacement and electric winning.

DESCRIPTION OF THE RELATED ARTS

Used printed circuit boards contain valuable metals such as silver, gold, copper and iron. If they are disposed of without recovering the valuable metals contained, it will be a hazard to the environment and loss of resources. Conventionally, the used printed circuit boards can be directly crushed before the valuable metals are recovered as disclosed in Taiwanese Patent Publication Nos. 247281 and 36904 for example. However, it consumes excessive energy because they contain a lot of elastic resin that is difficultly crushed to debris. Moreover, there are problems related to production of undesired dust and noise and wearing of machines.

Alternatively, the conventional burning method can be used for pretreatment. However, it takes much time and therefore expenses a lot of energy to burn the used printed circuit boards for low combustion efficiency.

As disclosed in Taiwanese Patent Publication No. 1268184, the used printed circuit boards are heated to a temperature higher than 200 degrees Celsius to melt solder on the used printed circuit boards so that electronic parts can be removed from the used printed circuit boards. Then, the electronic parts are submerged in a solvent and dissolved so that the valuable metals can be recovered.

Therefore, the present invention is intended to obviate or at least alleviate the problems encountered in prior art.

SUMMARY OF THE INVENTION

It is the primary objective of the present invention to provide an environmentally friendly method for recovering valuable metals from used printed circuit boards.

To achieve the foregoing objective, in the method, plasma is used to burn the used printed circuit boards, thus providing slag. The slag is grinded to debris smaller than 2 mm. A sieve with meshes of 0.149 mm is used to screen the debris into two fractions, the larger and the smaller ones. A magnet is used to separate ferromagnetic debris from non-ferromagnetic debris so that the ferromagnetic debris can be provided to a steel-making factory. The non-ferromagnetic large debris, which is rich in copper, can be provided to a copper refinery. The non-ferromagnetic small debris, which still contains valuable metals, can be further treated for recovering gold, silver and copper. 18N sulfuric acid is used to leach the debris. The solid/liquid ratio is retained at 10 g/50 ml, and the operational 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. The copper-contained primary leaching solution is subsequently separated from the primary sulfuric acid-leached residue and retained at 27 degrees Celsius for 48 hours for crystallization. 58.28% of the copper is precipitated and recovered in the form of copper sulfate crystals. The copper remained in the crystallization filtrate is replaced with iron powder, which is used as replacement reagent. 100% of the copper can be recovered as copper powder from the filtrate when iron is added at 100 times of the theoretical amount. 18N sulfuric acid is used to leach the primary sulfuric acid-leached residue again. 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 primary sulfuric acid-leached residue to the sulfuric acid after 2 hours. The secondary copper-contained leaching solution is then separated from the secondary sulfuric acid-leached residue. The copper in the solution is again replaced with iron powder so that copper is completely recovered when iron is added at 150 times of the theoretical amount. 8N nitric acid is used to leach the secondary 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 residue after 4 hours. Then the optimal silver-contained leaching solution is separated from the nitric acid-leached residue and using ammonia solution to adjust the pH value to 10. Subsequently 12N hydrochloric acid is provided for precipitation reaction. The ratio of the hydrochloric acid to the silver-containing leaching solution is 1:4 so that 100% of the silver is recovered in the form of silver chloride. The nitric acid-leached residue is then treated with 100% aqua liquid for recovering gold. The ratio of the residue to the aqua liquid is 0.5 g/50 ml, and the temperature is kept at 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. The solution is treated with zinc powder, as the replacement reagent, to recover about 99.43% of the gold from the optimal gold-contained leaching solution.

Other objectives, advantages and features of the present invention will become apparent from the following description referring to the attached drawings.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The present invention will be described via detailed illustration of the preferred embodiment referring to the drawing.

FIG. 1 is a flow chart of a method for recovering valuable metals from valuable metal-contained plasma-molten slag according to the preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, it reveals a method for recovering valuable metals from valuable metal-contained plasma-caused slag according to the preferred embodiment of the present invention. At 1, the slag is collected.

At 2, the slag is screened with a sieve with meshes of 0.149 mm. Thus, large debris 21 larger than 0.149 mm in size is separated from small debris 22 smaller than 0.149 mm in size.

At 3, the large debris 21 is tested with a magnet so that ferromagnetic debris 31 is separated from non-ferromagnetic debris 32. The ferromagnetic debris 31 can be provided to a steel-making factory. The non-ferromagnetic debris 32 is rich in copper and can be provided to a copper refinery.

At 4, the small debris 22 is tested with a magnet so that ferromagnetic debris 41 is separated from non-ferromagnetic debris 42. The ferromagnetic debris 41 can be provided to a steel-making factory.

At 5, primary sulfuric acid leaching occurs. The non-ferromagnetic debris 42 is leached with 18N sulfuric acid. During the leaching, the solid/liquid ratio is retained at 10 g/50 ml, and the temperature is kept at 70 degrees Celsius. After 1 hour of leaching, about 90.56% of the copper is released from the non-ferromagnetic debris 42 to the sulfuric acid. Primary copper-contained leaching solution 51 is separated from primary sulfuric acid-leached residue 52.

At 6, the copper-contained leaching solution 51 is retained at 27 degrees Celsius for 48 hours for crystallization. Thus, 58.28% of the copper is recovered in the form of copper sulfate crystals 61. The copper sulfate crystals 61 are separated from optimal crystallization filtrate 62.

At 7, the copper in the optimal crystallization filtrate 62 is replaced with iron powder that is used as replacement reagent 7. When the amount of the iron reaches 100 times of the theoretical value, 100% of the copper is recovered from the optical crystallization filtrate 62. Copper powder 71 is recovered.

At 8, secondary sulfuric acid leaching occurs. The sulfuric acid-leached residue 52 is leached with 18N sulfuric acid again. During the leaching, the solid/liquid ratio is retained at 50 g/50 ml, and the temperature is kept at 70 degrees Celsius. After 2 hours of leaching, about 100% of the copper is released from the sulfuric acid-leached residue 52 to the sulfuric acid. Then, secondary copper-contained leaching solution 81 is separated from secondary sulfuric acid-leached residue 82.

At 9, the copper in the secondary copper-contained leaching solution 81 is replaced with iron powder that is used as replacement reagent 9. When the amount of the iron reaches 150 times of the theoretical value, 100% of the copper is recovered from the secondary copper-contained leaching solution 81. Copper powder 91 is recovered.

At 10, the sulfuric acid-leached residue 82 is leached with 8N nitric acid. During the leaching, the solid/liquid ratio is retained at 1 g/50 ml, and the temperature is kept at 70 degrees Celsius. After 4 hours of leaching, about 100% of the silver is released to the nitric acid from the sulfuric acid-leached residue 82. Optimal silver-contained leaching solution 101 is separated from nitric acid-leached residue 102.

At 11, the pH of the optimal silver-contained leaching solution 101 is adjusted with ammonia solution.

At 12, 12N hydrochloric acid is used as precipitating agent. During the precipitation, the ratio of the hydrochloric acid to the silver-contained leaching solution 101 is 1:4. Thus, 100% of the silver is recovered in the form of silver chloride 121.

At 13, the nitric acid-leached residue 102 is leached with 100% aqua liquid. During the leaching, the ratio of the nitric acid-leached residue 102 to the 100% aqua liquid is 0.5 g/50 ml. The temperature is 70 degrees Celsius. After 4 hours, 100% of the gold is released to the aqua liquid from the nitric acid-leached residue 102, thus providing optimal gold-contained leaching solution 131.

At 14, the gold in the optimal gold-contained leaching solution 131 is replaced with zinc powder that is used as replacement agent. Thus, 99.43% of the gold is recovered from the optimal gold-contained leaching solution 131. Gold 141 is collected.

The method of the present invention exhibits several advantages. Firstly, gold, silver, copper and iron are rapidly recovered from used printed circuit boards. Therefore, the valuable metals can be processed in refineries and reused to reduce the waste of metals. Secondly, hazardous materials produced during the recovering of the valuable metals are reduced. Therefore, the hazard to the environment and human bodies is reduced.

The present invention has been described via the detailed illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims.

The present invention has been described via the detailed illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims.

Claims

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.