FONTANA DANILO (IT)
DE CAROLIS ROBERTA (IT)
PIETRANTONIO MASSIMILIANA (IT)
PUCCIARMATI STEFANO (IT)
GUZZINATI ROBERTA (IT)
TORELLI GIORGIA NADIA (IT)
| US4426225A | 1984-01-17 |
ANDREA MECUCCI AND KEITH SCOTT: "Leaching and electrochemical recovery of copper, lead and tin from scrap printed circuit boards", JOURNAL OF CHEMICAL TECHNOLOGY AND BIOTECHNOLOGY, JOHN WILEY & SONS LTD, UNITED KINGDOM, vol. 77, no. 4, 1 April 2002 (2002-04-01), pages 449 - 457, XP001577446, ISSN: 0268-2575, [retrieved on 20020208], DOI: 10.1002/JCTB.575
YANHUA ZHANG ET AL: "Current Status on Leaching Precious Metals from Waste Printed Circuit Boards", PROCEDIA ENVIRONMENTAL SCIENCES, vol. 16, 1 January 2012 (2012-01-01), pages 560 - 568, XP055121350, ISSN: 1878-0296, DOI: 10.1016/j.proenv.2012.10.077
| CLAIMS 1. A hydrometallurgy process for the recovery of materials from electronic boards comprising at least one leaching step (1) and one fractional precipitation step (4) to be performed on the solution resulting from the leaching step; said process being characterised in that, during said leaching step, the entire electronic board is immersed, for an amount of time ranging from 15 m to 48 h, in a leaching solution comprising HNO3 at a concentration that is higher than or equal to 20% by weight and with a solid/liquid ratio that is lower than or equal to 1; and in that it comprises a vibrating sieving step (2), in which the HNO3 solution resulting from the leaching step (1) is caused to flow through at least one first sieve having holes with a size ranging from 10 to 3 mm, in order to recover the unwelded components of different nature, and through at least one second sieve having holes with a size ranging from 0.5 to 0.01 mm, in order to recover metal Au; and a stannic oxide and/or stannic acid separation step (3), in which the leached resulting from the vibrating sieving step (2) is subject to a physical separation operation for the recovery of stannic oxide and/or stannic acid. 2. A hydrometallurgy process according to claim 1, characterised in that, during said leaching step, said HNO3 solution is at a concentration ranging from 25 to 35% by weight and is used with a solid/liquid ratio ranging from 1:1 to 1:4. 3. A hydrometallurgy process according to claim 2, characterised in that said HNO3 solution is used with a solid/liquid ratio ranging from 1:2 to 1:3. 4. A hydrometallurgy process according to any of the previous claims, characterised in that, during said leaching step (1), the leaching solution also comprises, besides HNO3, a peroxide compound . 5. A hydrometallurgy process according to claim 4, characterised in that said peroxide compound is hydrogen peroxide. 6. A hydrometallurgy process according to any of the previous claims, characterised in that said stannic oxide and/or stannic acid physical separation step (3) comprises a filtration operation and/or a decantation operation. 7. A hydrometallurgy process according to any of the previous claims, characterised in that the vibrating sieving step (2) involves a three-dimensional oscillating and/or linear and/or circular and horizontal and/or sussultatory-rotating vibration . 8. A hydrometallurgy process according to any of the previous claims, characterised in that said fractional precipitation step comprises, in sequence, a first operation (a), in which H2S04 or, alternatively, Na2S04 is added to the leached resulting from the stannic oxide and/or stannic acid separation step (3), thus causing the precipitation of PbSC>4; a second operation (b) , in which NaCl is added to the solution resulting from operation (a) , thus causing the precipitation of AgCl; a third operation (c) , in which OH" in a quantity that is sufficient to reach a pH ranging from 2.0 to 3.0 is added to the solution resulting from operation (b) , thus causing the precipitation of Fe (OH) 3; a fourth operation (d) , in which OH" in a quantity that is sufficient to reach a pH ranging from 3.2 to 6.0 is added to the solution resulting from operation (c), thus causing the precipitation of CuO or Cu (OH) 2. 9. A hydrometallurgy process according to any of the previous claims, characterised in that it comprises a residual board treatment step (5) for the treatment of the residual boards resulting from the leaching step (1); said residual board treatment step (5) comprising, in sequence, a first operation (a' ) , in which the residual board resulting from the leaching step, after having been washed, is ground so as to obtain fragments with a size smaller than 5x5 mm; a second operation (b' ) , in which the ground board is immersed, for an amount of time smaller than 48 hours, in HNO3 solution at a concentration that is higher than or equal to 20% by weight and with a solid/liquid ratio that is lower than or equal to 1; a third operation (c' ) , in which a quantity of OH" that is sufficient to reach a pH ranging from 3.0 to 12.0 is added to the HNO3 solution resulting from operation (b' ) , thus causing the precipitation of Cu(OH)2. |
TECHNICAL FIELD
The present invention concerns a hydrometallurgy process for the recovery of materials from electronic boards.
BACKGROUND ART
The recovery of materials from waste electrical and electronic equipment (WEEE) represents a great opportunity in terms of both the high value of some of these materials and their re ¬ use in components and products characteristic of the advanced economies (electric cars, flat-screen televisions, mobile phones, magnets, batteries, fuel cells, catalytic converters, some types of solar cells) .
The demand for these materials over the last few years has seen a sharp increase and has led to a critical situation in supply availability, consequently resulting in price increases .
For a correct evaluation of the above, it must be added that waste electrical and electronic equipment has a growth rate of 3-5% per year and that according to the European Waste Catalogue (EWS) , WEEE must be considered hazardous for the environment since it contains heavy metals and halogenated organic compounds.
The study of technologies for the recovery of raw materials from discarded electronic devices is therefore of great interest, in terms of both suggesting an alternative to disposal in land-fills or incinerators, thus preventing consequent pollution, and developing a selective recovery process of the metals having a high commercial value, also in relation to the possibility of exploiting them as alternative resources .
Electronic boards constitute on average 10% by weight of a PC, comprising mother board, RAM and CPU. Each board can contain up to 60 elements of the periodic table including a substantial proportion of noble and strategic metals like Pt, Ag, Au, in addition to metals with a high commercial value like Cu and Sn. The recovery of metals and materials from electronic boards generally entails mechanical pre-treatment of the boards (grinding) and is performed with physical, gravimetric and/or electromagnetic methods, pyrometallurgical , hydrometallurgical and biometallurgical processes.
Pyrometallurgical processes at high temperature (around 1200°C) require huge investments and involve significant environmental problems due to emissions into the atmosphere. Hydrometallurgical techniques, on the other hand, are generally performed at temperatures close to ambient temperature, with lower costs and limited atmospheric emissions .
Furthermore, the need for mechanical pre-treatment of the boards represents a complication both in terms of preparation of the sample and the subsequent hydrometallurgical process, to the extent that it is often necessary to design machinery able to crush the waste into suitable dimensions. Generally, gold is separated via a sequence of steps necessary for achieving a high purity level. The obtaining of gold and noble metals in general is the subject of various studies in the sector, and a part of the patent literature describes extraction processes conducted with the help of a complexing molecule synthesised for the purpose. The Applicant has devised a hydrometallurgical process for the recovery of materials from electronic boards. The main advantages of this process are that it does not require any grinding pre-treatment and is therefore performed on the whole electronic boards, and it guarantees simple direct recovery of the metallic gold and the stannic oxide and/or stannic acid following a first leaching step.
DISCLOSURE OF INVENTION
The subject of the present invention is a hydrometallurgical process for the recovery of materials from electronic boards, the essential characteristics of which are reported in claim 1, and the preferred and/or auxiliary characteristics of which are reported in claims 2-9.
BRIEF DESCRIPTION OF THE DRAWING
An embodiment example is given below for purely illustrative non-limiting purposes with the help of the attached figure which is a block diagram of the process subject of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
EXAMPLE LEACHING (1)
An electronic board as is was immersed for 4h in a leaching solution of HNO 3 at 30% by weight with a solid/liquid ratio of 1:3, and then removed.
The purpose of this leaching stage is to remove the weldings, dissolve the metals, precipitate the stannic oxide and/or stannic acid and detach the gold in metallic form from the circuits.
Alternatively to the above, the leaching solution, in addition to the nitric acid, can also contain a peroxide compound, preferably hydrogen peroxide. VIBRATING SIEVING (2)
Here and below, by the term vibrating sieving we mean a solid/liquid and solid/solid separation operation by means of vibrating sieves, based on the different sizes of the component parts of the solid. The sieves, provided with holes of suitable diameter and arranged in series, separate the materials by "piece size" .
At the end of the 4 h of the leaching stage, the leached was subject to a vibrating sieving stage. The leached was passed through a vibrating sieve comprising 4 sieves with holes of decreasing size (10 mm; 5 mm; 0.4 mm; 0.03 mm), which retain solids with progressively smaller size. The fractions recovered at this stage are (in order of decreasing size) :
- unwelded components of different nature (slots, capacitors etc.)
- gold in metallic form in the presence of plastic materials and fibreglass of the same size, to be mechanically separated.
In this way, directly from the combination of treatment with the HNO 3 solution and a vibrating sieving stage, metallic gold was recovered in a distinct form and conditions were obtained allowing separation of the stannic oxide and/or stannic acid by means of physical methods.
The common recovery of the stannic oxide and stannic acid is due to the fact that, as known to a person skilled in the art, stannic oxide is in equilibrium with stannic acid as a function of its hydration .
SEPARATION OF STANNIC OXIDE AND/OR STANNIC ACID (3)
The leached resulting from the vibrating sieve is subject to a physical separation stage to recover the stannic oxide and/or stannic acid. In particular, the stannic oxide and/or stannic acid is separated by means of a decantation and/or filtration operation. FRACTIONAL PRECIPITATION (4)
The leached resulting from the stannic oxide and/or stannic acid separation was treated with the addition of chemical reagents to cause a series of fractional precipitations. This stage comprised the following operations:
a) 400 cc of H 2 SO at 96% by weight per litre or, alternatively, 100 g of Na 2 S0 4 per litre, were added to the leaching, causing the precipitation of PbS0 4 ;
b) addition of 0.4 g of NaCl per litre of solution resulting from operation (a), causing the precipitation of AgCl;
c) addition of NaOH to the solution resulting from operation (b) in a quantity sufficient to reach a pH of 2.80, causing the precipitation of Fe (OH) 3 ;
d) addition of NaOH to the solution resulting from operation (c) in a quantity sufficient to reach a pH equal to 5.30, causing the precipitation of CuO or Cu (OH) 2 depending on whether H2SO 4 or Na 2 S0 4 were used respectively in operation (a) .
In each of the operations (a) - (d) the precipitates were recovered by filtration.
In this fractional precipitation stage it is possible to intervene on the pH value of the individual operations to satisfy the degree of purity required for the individual products.
The AgCl recovered by the operation (b) was subject to chemical reduction, dissolving the precipitate in 20 cc of NaOH at 50% by weight per gram of AgCl and for each ml of the solution obtained, 35 mg of glucose were added. In this way the metallic Ag was obtained.
The Cu (OH) 2 or the CuO obtained as precipitate from the operation (d) was re-dissolved in a solution of H 2 S0 4 at 50% by weight (1 mL for every g of precipitate) , and the copper was obtained in metallic form by means of subsequent electrodeposition. RESIDUAL BOARD TREATMENT (5)
The residual board resulting from the leaching stage is subject to a treatment stage for the recovery of metallic Cu. This treatment stage comprises the following operations:
a' ) after washing, the residual board was ground into fragments of dimensions 4x4 mm;
b' ) the ground board was immersed for 4 h in a solution of HNO 3 at 30% by weight with a solid/liquid ratio of 1:3;
c' ) a quantity of NaOH sufficient to reach pH of 5.30 was added to the leachedresulting from operation (b' ) , causing the precipitation of Cu(OH) 2 .
As described above, the precipitated Cu (OH) 2 is re-dissolved in a solution of H 2 S0 4 at 50% by weight (1 mL for every g of precipitate) , and by means of subsequent electrodeposition the copper was obtained in metallic form.
From the above description, it can be immediately seen that the process of the present invention is able to guarantee simple efficient recovery of the metals in the electronic boards, without subjecting the same to grinding pre-treatment, which necessarily involves advantages in both production and process terms. Furthermore, the process subject of the present invention guarantees an immediate recovery of the gold following the sole combination in series of treatment of the whole board with a solution of HNO 3 in given conditions and vibrating sieving of the leaching, and recovery of the stannic oxide and/or stannic acid following a subsequent physical separation.
Furthermore, the process of the present invention offers the advantage of being able to intervene in the recovery conditions of the metals to obtain the latter with the desired degree of purity.
Lastly, the process of the present invention has the great advantage of not suffering from application limitations according to the metals present in the electronic boards. In fact, the process of the present invention can also be performed on electronic boards containing materials such as lead, which can often be an obstacle to the effectiveness of hydrometallurgical processes for the recovery of metals from electronic boards.
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