Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Recycling electrolytic product produced during synthesis...
Reexamination Certificate
2001-10-10
2003-11-04
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Recycling electrolytic product produced during synthesis...
C205S580000, C205S582000, C205S599000, C205S601000, C205S611000, C205S613000, C205S614000
Reexamination Certificate
active
06641712
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to a method for recovery of tin, tin alloys or lead alloys, such as solder, from printed circuit boards.
BACKGROUND OF THE INVENTION
With the advent of more and more electronic hardware, there is more and more electronic scrap produced, including scrap printed circuit boards. Furthermore, there is a growing need for more environmentally friendly methods of recycling scrap printed circuit boards. Many current commercial processes focus only on recovering some of the component parts of printed circuit boards. For example, printed circuit boards are heated in furnaces to pyrolyze the organic compounds and melt the metals. The plastics and the electronic components are destroyed producing potentially harmful fumes and a remaining complex mixture of metals that then needs to be separated. An alternative process comprises the selective removal of the higher value components, such as gold edge connectors and microprocessor chips, and then scrapping the rest of the printed circuit board to, for instance, landfill.
It is more likely than not that legislation will be planned and enacted, particularly in the European Community, that will require manufacturers of electronic equipment to take back equipment at the end of its useful life for recycling. There is, therefore, a need for a method for treating printed circuit boards that can recover the majority of the cornconent parts of scrap printed circuit boards without the production of undesirable waste products.
During the manufacture of printed circuit boards, solder is applied at various stages for the purpose of bonding components to the exposed areas of metal using a wave soldering technique or using a solder paste. Furthermore, during the formation of lines and pads on printed circuit boards, a layer of tin or a tin-lead alloy, such as solder, may be deposited by circuit boards, a layer of tin or a tin-lead alloy, such as solder, may be deposited by electrodeposition, immersion plating or other processes onto selected areas of copper surfaces of circuit boards to define conductive tracks, pads, through holes, etc., and to act as an etch resist during subsequent etching array of the copper surfaces. Thus, in a method for recycling of scrap printed circuit boards the selective dissolution of the tin or tin-lead alloy used in the manufacture of the printed circuit boards from the copper substrate surface, without dissolving the copper, is an important first step.
European Patent No. EP-0508960 discloses a method of producing metallic lead from a material containing lead by dissolving the lead contained in the material and an electrolysis step for the cathodic deposition of the dissolved lead. The dissolving step is carried out with the use of an acid electrolyte in the presence of a redox couple. The method is used, in particular, for the production of lead from the active material of spent accumulators. Although this process discloses the dissolution of lead, a process for the selective dissolution of tin or tin-lead alloys is still desired.
A new selective dissolution process has now been developed in which the Plastics associated with electronic components are not attacked, the electronic components are not affected by the oxidant solution used in the process and the identification coding on the electronic components is unaffected. Thus, the components can be recovered for use. Furthermore, the oxidant solution, which is used to dissolve the tin or tin-lead alloy, is regenerated and recycled to the method, thereby avoiding the production of undesirable or unwanted waste products.
SUMMARY OF THE INVENTION
Embodiments of the invention provide a method for selective dissolution of tin and/or lead or tin-containing alloys from printed circuit boards without substantial dissolution of copper or precious metals and without attack on plastics associated with electronic components mounted to printed circuit boards, the method comprising steps of:
(i) providing a solution comprising Ti(IV) and an acid which forms stable and soluble salt of Ti(III), Ti(IV), Sn(II) and Pb (II);
(ii) contacting a printed circuit board with the solution under anaerobic conditions for a time sufficient to effect dissolution of substantially all of the Sn and/or Pb- or Sn-containing alloy therefrom, as Sn(II) and/or Pb(II);
(iii) subjecting the solution from step (ii) to electrolytic reduction in order to recover substantially all of the Sn(II) and/or Pb(II) species contained therein as Sn and/or Pb; and
(iv) oxidizing the solution from step (iii) to regenerate the oxidant metal species and recycling the regenerated solution to step, (i) of the process.
By the term “soluble salt” as used herein is meant that the salt has a solubility of at least 1 gram per liter in the solution at the temperature at which the process is carried out.
For use in step (ii) of the method according to the invention, the oxidizing solution will preferably oxidize tin and lead metals, but will not dissolve copper. For this to be achieved the solution redox potential should be in the range of from +0.342 volts to ÷0.126 volts (standard hydrogen electrode), in terms of standard electrode potential, i.e. the interval between the anodic dissolution of copper and tin/lead.
The preferred solution for use in step (ii) of the method comprises an acid selected from the group consisting of fluoroboric acid, fluorosilicic acid, hexafluoro-phosphoric acid, hexafluoroantimonic acid and an alkylsulphonic acid. A solution comprising Ti(IV) and fluoroboric acid is particularly preferred. This solution may be prepared by dissolving Ti metal in fluoroboric acid with a sparge of oxygen gas or air. This solution has an unexpected selectivity for the dissolution of Sn and Pb over other metals, particularly copper.
In one embodiment of the method of the invention, other oxidant species/acids as defined in step (i) may also be used provided that, in use, the oxidant ions in solution have an oxidation potential which can selectively dissolve tin or a tin-lead alloy from the surface of the printed circuit board, but does not oxidize copper metal. Step (ii) of the method is carried out anaerobically, for example, by sparging the leach solution with an inert gas, such as nitrogen, during the leaching step.
The solution used in step (ii) of the method preferably comprises the oxidant metal species at a concentration generally in the range of from 0.01 M to 1.0 M metal ions, preferably 0.5 M to 0.9 M metal ion, and the acid at a concentration in the range of 10% to 100% by weight acid.
The temperature at which the solution used in step (ii) is contacted with the substrate surface is generally from 0° C. to 60° C., and preferably 20° C. to 30° C.
The method according to the invention may be used to dissolve tin or tin-lead alloys from printed circuit boards. Alloys which can be dissolved generally comprise from 5 to 99.5% by weight Sn, up to 95% by weight of Pb, and optionally up to 5% by weight of one or more of Ag, Bi, In, Zn, Cu or Sb. Solders commonly used in printed circuit board manufacture comprise 63% Sn, 37% Pb by weight, or 62% Sn, 36% Pb, 2% Ag by weight. Aluminium and any iron present in the printed circuit boards will dissolve in the acid leach and reduce the Ti(IV) oxidant to Ti(III), thus leaving less Ti(IV) available to react with the solder.
Accordingly, it is advantageous to remove these metals from the scrap printed circuit board prior to treatment with the leach solution. For example, physical separation methods may be used, such as by magnetic means for iron and using an eddy current separator for aluminium.
In step (iii) of the method of the invention, the electrolytic reduction of the solution containing the dissolved species is preferably carried out in a divided cell with inert electrodes, such as graphite anodes and stainless steel cathodes, and anolyte and catholyte compartments separated by a membrane, such as microporous or ion exchange material. The solution containing the dissolved species comprises the catholyte and th
Dalrymple Ian McCrady
Fray Derek John
Gibson Robert William
Goodman Paul David
Holt Lyn
Alpha Fry Limited
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
Valentine Donald R.
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