Container for corrosive materials

Abstract: A container in which minerals such as copper are purified in an electrolytic process includes bottom, end and side walls for containing a corrosive electrolyte, such as, a sulphuric or hydrochloric acid solution. The bottom, end and side walls of the container are composed of a cured mixture of 10-19 percent of a modified, vinylester or polyester thermo-setting resin and the balance consisting of 1/4"-1/64" inch crystalline silica, fine silica sand or silica flour and glass beads approximately four microns in size and/or mica flakes about 1/64" in size or 1/4"-1/8" chopped fiber glass strands. The container is formed in a continuous pouring process and includes nonconductive reinforcing rods.

Description: BACKGROUND OF THE INVENTION This invention relates to containers for highly corrosive solutions and more particularly to containers for use in the electrolytic refinement or electrowinning of metals such as copper. In one type of process, the refinement of metals such as copper, a substantially pure copper anode is immersed in a suitable electrolyte, such as, a hydrochloric or sulphuric acid solution. The copper is deposited in a pure form on a cathode when an electric current is passed between the electrodes. One type of prior art container employed for such electrolytic cells consists of a concrete shell having iron reinforcing bars and a lead or plastic liner. Such containers were not wholly satisfactory because the linings often failed causing the concrete to fail before the leaks were detected resulting in the loss of slimes and electrolyte. For this reason prior art concrete cells required high maintenance, high repair and replacement costs and caused excessive downtime and lost production. In addition, the iron reinforcing bars provide a leakage path to stray electric currents which reduced current efficiency and affected cathode quality. Furthermore, because prior cells tended to absorb highly toxic materials, environmental concerns result in high disposal costs. One prior art effort to improve such electrolytic cells included a shell fabricated from a mixture of about 20 percent resin and 80 percent various aggregates such as pea size gravel, fine silica sand, silica flour and one-quarter to one-eighth inch chopped fiber glass strands. These prior art cells had the disadvantage of relatively high fabrication costs, and a susceptibility to short circuiting as a result of the use of reinforcing rods which include ferrous materials. Another disadvantage of prior art cells was that the molding process by which they were formed resulted in cold joints, irregular internal surfaces and required that overflow boxes be separately attached. From US-A-3,920,603, there are known reinforced resin compositions are articles formed thereof. In particular, reinforced synthetic polyester resin compositions are disclosed, having 10-60% by weight of resin, 1-30% by weight of glass spheres, 10-60% by weight of mica platelets, and 20-70% by weight of aluminum trihydrate particles. Said compositions may be applied to a mould or to a plastic sheet and as these compositions do not require glass fibers, these materials avoid the laborious rolling down of fibers carried on the surface of freshly applied glass fiber resin compositions. The aforementioned US patent teaches that for spraying purposes, the resin must be about 30-60% by weight. Moreover, said prior art reference states that between 10% and 20% resin contents, the composition is no longer sprayable. It is an object of the invention to provide an improved container for a corrosive electrolyte used in an electrolytic process. Furthermore, it is an object of the present invention to provide a method of manufacturing such an improved container. In terms of a container, the above object is achieved by the subject matter of claim 1. Preferred embodiments and further improvements are indicated in claims 2, 3 and 4. In terms of a method, the above object is achieved by the subject matter of claim 5. Preferred embodiments and further improvements of the inventive manufacturing method are indicated in claims 6 and 7. The inventive container is economical and furthermore, minimises the likelihood of short circuits. Furthermore, the inventive container does not require a lining but permits operation at higher temperatures and higher condensities and furthermore, permits greater electrolyte flow. Thinning agents are known in the art as materials added to polymer resins to lower the viscosity thereof (such as styrene and styrene monomer). BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a side elevational view partly in section showing a cell according to my invention; FIGURE 2 is a top plan view thereof; and FIGURE 3 is a view taken along lines 3-3 of FIGURE 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The invention relates to a cell for containing a corrosive liquid such as the electrolyte employed in an electroplating operation. As those skilled in the art will appreciate, electrolytic cells employed for purifying metals, such as copper, consist of a container for an electrolyte, such as a sulfuric or hydrochloric acid solution. One process uses an anode consisting of relatively pure copper, i.e., about 99% copper, and a starter sheet of a purer copper or other suitable material, which are immersed in an electrolyte. The anode and starter sheet or cathode are placed in series with an electrical energy source so that the passage of current between the anode and cathode and through the electrolyte causes copper ions to flow from the anode through the electrolyte to the cathode. This provides a body of copper at the cathode which is 99.9% pure. Precious metals such as gold, silver, platinum, and other metals and by-products collect in a sludge which forms at the bottom of the cell. A cell 10 according to the invention is shown in the drawings to include a bottom 12, side walls 13 and 14 and end walls 15 and 16. An overflow box 17 is integrally cast on end wall 16. The walls 13, 14, 15 and 16 taper from bottom to top as molded. A matrix of reinforcing bars 18, of a nonconductive material, such as FRP fiber glass, is disposed in the bottom 12 and extends partially up the side and end walls 13, 14, 15 and 16. Electrolytic cells of the type discussed above must be nonporous and possess sufficient mechanical strength and must be chemically inert relative to the electrolyte which comprises a sulfuric or hydrochloric acid solution. The cell according to the preferred embodiment of the present invention comprises a mixture of 10%-19% by weight of a modified vinylester or polyester thermo-setting resin, and the balance consists of a mixture of crystalline silica particles, and particles taken from the group consisting of mica flakes, glass beads and chopped fiber glass strands. The vinylester or polyester resin is thinned to reduce viscosity and permit higher filler loading. The viscosity of the vinylester or polyester resin should be less than 200 CPS as measured by a Brookfield viscosity meter Model LVT at 25°C (77°F) with a 13 spindle at 60 RPM. According to one example, the components by weight of the modified vinylester resin are as follows: 80%-90% vinylester resin; 10%-20% styrene monomer (thinner); 1%-5% degassing agent; 0.2%-2% methyl ethyl ketone peroxide, or cumene hydroperoxide (catalyst) or benzoyl peroxide; 0.05%-.2% inhibitor; 0.2%-.6% cobalt napthalate (6%) (promoter) 0.02%-.5% dimethyl aniline (100%) (accelerator); Any suitable inhibitor, such as 2.4 pentanedione may be employed and any suitable degassing agent such as xylene or acetone may be used. The dry mixture comprises: 40%-60% 3.17 mm - 6.35 mm (1/8"-1/4") crystalline silica 10%-25% 1.58 mm - 3.17 mm (1/16"-1/8") crystalline silica 10%-15% 0.79 mm - 1.58 mm (1/32"-1/16") crystalline silica 10%-15% fine silica sand 1% mica flakes Chopped fiber glass strands 3.17 mm - 6.35 mm (1/4"-1/8") or glass spheres can be substituted for the mica flakes. The proportions of resin and dry ingredients by weight in the final mixture, according to the Preferred embodiment of the invention, are as follows: 10%-19% modified vinylester or polyester resin 40%-60% 3.17 mm - 6.35 mm 1/8" - 1/4" crystalline silica 10%-25% 1.58 mm - 3.17 mm (1/16" - 1/8") crystalline silica 10%-15% 0.79 mm - 1.58 mm (1/32" - 1/16") crystalline silica 10%-15% fine silica sand or silica flower 0.9%-5% mica flakes, 3.17 mm - 6.35 mm (1/4'-1/8") chopped fiber glass strands, and/or glass spheres In one specific example a resin mixture was prepared with the following ingredients: 203,8 Kg (450 pounds) vinylester resin; 38.5 Kg (85 pounds) styrene monomer; 5.9 Kg (13 pounds) xylene; 0.68 Kg (1.5 pounds) methyl ethyl ketone peroxide; 6.8 Kg (15 ounces) pentanedione; 9.9 Kg (22 ounces) cobalt napthalate; 0.9 Kg 2 ounces dimethyl aniline 11.32kg (Twenty-five pounds) of the foregoing modified resin mixture was then mixed with the following quantities of dry ingredients: 45.3 Kg (100 pounds) 3.17 mm - 6.35 mm (1/8"-1/4") crystalline silica 18.12 Kg (40 pounds) 1.58 mm - 3.17 mm (1/16"-1/8") crystalline silica 9.06 Kg (20 pounds) 0.79 mm - 1.58 mm (1/32"-1/16") crystalline silica 9.06 Kg (20 pounds) fine silica sand 0.9 Kg (2 pounds) mica flakes, chopped fiber glass strands 3.17 mm - 6.35 mm (1/4" to 1/8") or glass spheres can be substituted for the mica flakes The resin acts as a binder for the dry materials and fills the interstices therebetween so that the container is impervious to the electrolyte solution and forms a corrosion-resistant material unaffected by the electrolyte solution. The chopped fiber glass strands, mica and/or glass spheres provide a tighter composite material which also reduces porosity and increases physical strength. The nonconductor reinforcing bars increase physical strength and allow the cells to be supported in only two areas if necessary. It was the practice to pour prior art cells in an upright mold. Because the inside bottom, side and end walls of the cell must be smooth to facilitate removal of the sludge, one common practice in molding prior art cells was to pour and trowel the bottom surface before continuing to pour the side and end walls. This sometimes resulted in a cold joint which adversely affected the physical strength of the cell and produced areas of leakage. The container according to the preferred embodiment of the invention is formed by mixing the resin and dry ingredients and then pouring the same continuously into an inverted mold. The mixture is then allowed to cure at room temperatures because an inverted mold is used, the inside bottom, side and end wall surfaces are in contact with a smooth mold surface. Accordingly, these surfaces will also be relatively smooth without troweling. This permits continuous casting of the cell to insure that no cold joints are formed. Casting the cell upside down also facilitates the casting of an integral overflow box with the cell. As a result, greater physical strength is achieved over prior art cells where the overflow box was cast separately and then attached to the cell. This prior art method caused leaks and made the overflow box susceptible to mechanical damage. Because of the strength of the cell made in accordance with the mixture and reinforcing bars discussed above, a cell wall thickness of about two and one half inches at the top and three and one half inches at the bottom is satisfactory for a conventional cell which is about sixteen feet in length, four and one half feet in height and four and one half feet in width. Conventional concrete cells have a wall thickness of about five to six inches. As a result, cells made in accordance with the present invention provides cells with a greater internal capacity for the same outside dimensions. Since the one factor in determining the electrorefining capacity of a refining facility is by the number of cells and their capacity, the use of cells having thinner walls significantly increases total plant capacity. A typical electrolytic refinery has capacity of approximately 120,000 tons per year. This capacity could increase, for example. by approximately 3,171,000 kg (7, 000,000 Pounds) Per year with the additional internal cell capacity. While the life expectancy of cells according to the present invention has not as yet been determined, it is estimated that as a result of their physical strength, impermeability and nonconductiveness, their useful life will be much longer than conventional concrete cells. In addition, any physical damage to cells according to the invention can be more readily repaired than prior art concrete cells, thereby reducing maintenance costs and production downtime. The operating temperature of some prior art cells was limited to about 71 °C (160°F) because the plastic linings employed tended to lose shape and reduce useful life at higher temperatures. With the cell according to the present invention, coupled with the use of nonconducting reinforcing rods, higher current densities and temperatures can be employed, thereby increasing production rates, quality and capacity. Bars of elongate and preformed nonconductive material, such as, for example, precured fiber glass are preferably inserted into the bottom and side walls and corners of bottom-side and bottom-end wall corners of the container as the same is being poured thereby substantially increasing the physical strength properties and minimizing the possibility of electrical short-circuiting due to the use of metallic reinforcing bars in prior art containers. Such reinforcing lap boards which support the bars permit the electrodes to be mounted directly on the cell wall, thereby eliminating the necessity for an insulating board as in prior art devices. While only a single embodiment of the invention is described herein, it is not intended to be limited thereby but only by the scope of the appended claims.

Claims: A container for a corrosive electrolyte used in an electrolytic process, characterised in that said container consists of a cured mixture of 10%-19% by weight of a resin taken from the group consisting of vinylester and polyester thermo-setting resin modified by the addition of a thinning agent and the balance consisting of crystalline silica particles and particles taken from a group consisting of glass beads, chopped fiber glass strands and mica flakes; wherein the crystalline silica comprises a mixture of 80%-90% by weight particles which are 0.79mm to 6.35mm (1/4"-1/32") in size, 10%-15% by weight particles taken from the group consisting of fine silica sand silica flour and 1%-5% by weight particles taken from the group consisting of glass beads mica flakes and chopped fiber glass strands; wherein the modified resin comprises 80%-90% of a resin taken from the group consisting of vinylester and polyester resin and the balance a thinning agent, inhibitors, promoters and a catalyst. The container set forth in claim 1, further characterised in that the crystalline silica comprises 40%-60% by weight particles which are 3.17mm to 6.35mm (1/4"-1/8") in size, 10%-25% by weight particles which are 1.58mm to 3.17mm (1/8"-1/16") in size and 10%-15% by weight particles which are 0.79mm to 1.58mm (1/16"-1/32") in size, 10%-15% fine silica sand or silica flour and including 0.9%-5% by weight mica particles taken from the group consisting of glass beads 4µm in size, mica flakes about 0.39mm (1/64") in size and 3.175mm to 6.35mm (1/4"-1/8") chopped fiber glass strands. The container set forth in claim 2 further characterised in that reinforcing bars of a nonconductive material molded into the walls and bottom of the container. The container set forth in claims 1 or 3 further characterised in that the viscosity of the modified resin is less than 200 CPS as measured by a Brookfield viscosity meter Model LVT at 25°C (77°F) with a #3 spindle at 60 RPM. A method of manufacturing the container set forth in claim 1, characterised in that said method comprises the steps of mixing 10%-19% by weight of a thermo-setting resin taken from the group consisting of vinylester and polyester resin modified by the addition of a thinning agent, inhibitors, promoters and catalyst and the balance consisting of crystalline silica particles and particles taken from a group consisting of chopped fiber glass strands and mica flakes, and continuously pouring the mixture into an inverted mold which defines bottom, ends and side walls and allowing said molded mixture to cure whereby the inner surfaces of the container will contact the mold surfaces so that smooth inner surfaces will be molded, wherein the crystalline silica comprises a mixture of 80%-90% by weight of particles which are 0.79mm to 6.35mm (1/4"-1/32") in size, 10%-15% by weight particles taken from the group consisting of fine silica sand silica flour and 0.9%-5% by weight of particles taken from the group consisting of glass beads about four microns in size, mica flakes about 0.39mm (1/64") in size and chopped fiber glass strands 3.17mm to 6.35mm (1/4"-1/8") in size; wherein the modified resin comprises 80%-90% of a resin taken from the group consisting of vinylester and polyester resin and the balance a thinning agent, inhibitors, promoters and catalyst. The method set forth in claim 5, further characterised in that the crystalline silica comprises 40%-50% by weight particles which are 3.17mm to 6.35mm (1/4"-1/8") in size, 10%-25% by weight particles which are 1.58mm to 3.17mm (1/8"-1/16") in size and 10%-15% by weight particles which are 0.79mm to 1.58mm (1/16"-1/32") in size, 10%-15% particles taken from the group consisting of fine silica sand and silica flour. The method set forth in claims 5 or 6, further characterised in that the step of molding an overflow box integrally with said container.

Inventors: HARRY JOHN O, VERHAGEN GEORGE, HARRY, JOHN O., VERHAGEN, GEORGE
Applicants: CORROSION IP CORP, CORROSION IP CORPORATION
Application year: 1989
Main classification: C08L67
IPC codes: C25C7, C25B9, C08K7, C08K3, C08L67