United States Patent (19) 11 Patent Number: 5,026,530 Drinkard, Jr. et al. 45) Date of Patent: Jun. 25, 1991

54 METHOD FOR PRODUCING COPPER ARSENATE COMPOSTIONS FOREIGN PATENT DOCUMENTS

69011 5/1974 Australia ...... 4236O2 75 Inventors: William F. Drinkard, Jr., Charlotte; 627083 8/1978 U.S.S.R...... 423/602 Hans J. Woerner, Mt. Pleasant, both 101029 2/1917 United Kingdom ...... 423/602 of N.C. 445840 1/1935 United Kingdom ...... 423/6O2 Primary Examiner-Wayne A. Langel 73) Assignee: Drinkard Developments, Charlotte, Attorney, Agent, or Firm-Ralph H. Dougherty N.C. (57 ABSTRACT 21 Appl. No.: 502,564 A method of preparing copper arsenate compositions having unique advantges in lower cost and higher per 22) Filed: Mar. 30, 1990 formance for use in preparing chromated copper arse nate wood preserving formulations. These copper arse 51 Int. C...... CO1G 28/02 nate compositions are insoluble copper arsenate in 52 U.S. C...... 423/87; 423/601; water or as a dry reactive powder, have a mol ratio of 423/602 As2O5 to CuO of 1:4, and is readily soluble in chromic 58) Field of Search ...... 423/601, 602, 87 acid to form CCA wood preservatives. This copper arsenate is prepared by reacting suitable copper-bearing 56 References Cited materials with arsenic trioxide and air or oxygen in U.S. PATENT DOCUMENTS ammoniacal solutions. Either or both of the starting raw 1,085,898 2/1914 Fischer ...... 42.3/601 materials, i.e., the copper and the arsenic, may be very 1,517,516 12/1924 Lloyd et al. . ... 42.3/602 impure, which impure materials were heretofore unsuit 1,596,662 8/1926 Jenkins et al...... 423/602 able for the production of copper arsenate. 2,112,102 3/1938 Klumpp ...... 423/602 2,573,252 10/1951 Farber ...... 423/601 24 Claims, No Drawings 5,026,530 1. 2 METHOD FOR PRODUCING COPPER ARSENATE OBJECTS OF THE INVENTION COMPOSITIONS It is the principal object of the present invention to provide a method for improving the environmental and FIELD OF INVENTION economic quality of CCA. It is also an object of this invention to provide a The present invention relates to the production of method for producing a high purity copper arsenate. copper arsenate, and more particularly to the produc It is also an object of this invention to provide a tion of copper arsenate from starting materials including method for producing a high purity copper arsenate arsenic trioxide and copper, either or both of which can O which will free CCA manufacturers from their present be impure. The resulting copper arsenate is, however, dependence on a limited number of suitable purity cop purer than those produced by other processes for cop per and arsenic sources. per-chrome-arsenic (CCA) timber preservatives. Thus, It is also an object of this invention to provide a the invention offers dual advantages: the ability to use method for producing a high purity copper arsenate lower cost, more abundant raw materials while simulta 15 which will significantly lower the cost of both copper neously improving the performance of the resulting and arsenic raw materials. It is also an object of this invention to provide a CCA wood preservative. method for producing a high purity copper arsenate BACKGROUND OF THE INVENTION which will allow the use of very impure arsenic raw 20 materials, such as those presently being wasted and It has been common to prepare copper and chrome stored underground by gold and copper refiners. arsenic compositions for use as timber preservatives It is also an object of this invention to provide a from chromic acid, copper oxide and arsenic acid start method for producing a high purity copper arsenate ing materials. In such a process, the arsenic acid may be which will allow the use of off-grade copper sources, derived from arsenic trioxide, but such arsenic trioxide 25 not only copper scrap, but also copper associated with must be particularly pure, otherwise the impurities iron by-products and scrap products which sell for therein would be carried through the process into the significant discounts below copper scrap prices. arsenic acid solution. It is also an object of this invention to provide a When such contaminated arsenic acid is used in the method for producing a high purity copper arsenate manufacture of CCA, the impurities become insolubil 30 which will allow the direct use of many copper and ized in the CCA wood treating solution. The resulting arsenic containing by-products from industrial and min precipitate not only represents an economic loss, but it ing operations without the need to purify these before may block pumps, valves and other portions of the using them in our process. handling and treating equipment. In addition, because 35 It is also an object of this invention to provide a pro of the chrome and arsenic content of CCA wood pre cess that may be operated without atmospheric dis servative, these precipitates represent a significant envi charge of waste. It is also an object of this invention to provide a pro ronmental hazard. cess that may be operated without solid waste dis Although many acid-soluble substances such as cal charge. cium, aluminum, etc., are undesirable, the major prob It is also the object of this invention to provide a lem-causing precipitate is acid solubilized iron. method for producing a high purity copper arsenate As presently formulated, CCA preservatives cannot from arsenic trioxide, copper and oxygen, the steps of use copper metal as a raw material, because the copper which method may be performed separately or may be metal would reduce the chronic acid causing total 45 performed in a combination of two or more steps to precipitation of the CCA. Since copper oxide and other gether. suitable copper forms of raw materials for CCA manu It is also an object of this invention to provide a facture, such as copper carbonate, are manufactured method for producing a high purity copper arsenate from copper metal, they always command a premium which will convert ammonium arsenite to cuprammo price above the base metal. Such prices, traditionally, 50 nium arsenate in a single reaction. are 50% to 100% higher than the base copper metal price. SUMMARY OF THE INVENTION Processes have been invented that allow the use of The present invention is a process for the production copper metal directly in the oxidizing arsenic acid pro of copper arsenate, which comprises: (a) reacting ar 55 senic trioxide with aqueous ammonia to produce ammo cess, but, unlike the present invention, all of these pro nium arsenite solution; (b) reacting the ammonium ar cesses, because of their acidic nature, require a very senite solution so produced with copper and cupric ion pure form of copper. Any iron or other acid soluble in the presence of oxygen to produce cuprammonium impurity present in the copper or arsenic starting raw arsenite; (c) reacting the cuprammonium arsenite so materials will be found in the copper arsenate formed 60 produced with copper in the presence of oxygen and a by these processes and carried by it into the CCA caus catalyst to produce a copper ammonium arsenate solu ing precipitation. tion, and d) removing ammonia and recovering a slurry During the past twenty years, there have been many of copper arsenate. occasions when suitable arsenic trioxide for arsenic acid The copper arsenate produced by this process is dif manufacturing was in very short supply, either it was 65 ferent from the copper arsenate produced by acidic not available or available only at exorbitant prices. Such processes, which are blue and have the chemical for supply and price difficulties have applied equally to mula ranging from (2.5CuO:As2O5XH2O) to suitable copper and copper oxide materials. (3.5CuO:As2O5XH2O). The copper arsenate of the 5,026,530 3 4. present invention has the chemical formula 4CuO:As verts the cuprammonium arsenite to cuprammonium 205XH2O, and has a green color. arsenate, again in the presence of oxygen and a catalyst. We have found that potassium iodide at a concentra DETAILED DESCRIPTION OF THE tion of 1 ounce per 1,000 gallons of aqueous ammonia is INVENTION the best catalyst to use, although other halides, particu Initially, arsenic trioxide is reacted with aqueous larly iodides, bromides, and chlorides, also have a pro ammonia which has been recovered from stripping the moting effect. cuprammonium arsenate to produce ammonium arsen While the second and third reactions can be consid ite. Crude arsenic trioxide, containing substantial impu ered a two stage process, we have discovered that they rities, may be used instead of pure arsenic trioxide. The 10 can be performed as a single step. impurities of crude arsenic trioxide that cause precipita The copper used in the second reaction can be a tion and other problems in CCA solutions, such as iron, primary copper, such as copper wire, cathodes, or the are insoluble in the ammonium arsenite solution and like. However, it need not be a pure copper, but can be may be easily filtered out. The crude arsenic trioxide copper scrap or iron-containing (bi-metallic) copper can be in a form derived from well known arsenic con 15 scrap, such as armatures from electric motors. Various taining ores and residues, for example, the 80 to 90% mine products, such as cement copper and various cop arsenic trioxide that is commonly captured by electro per and arsenic precipitates may also be used. Waste or static precipitation from gold and copper refining oper byproduct metal arsenides or arsenates can also be uti ations. lized in the invented process. Metal arsenides must be To minimize equipment size and to maintain the 20 added to the copper-oxidation reaction which will oxi water balance needed to avoid discharge from this pro dize the arsenic present in the arsenide form to the cess, it is desirable to carry out the reaction at tempera arsenate form. When the arsenide is copper, a reduction tures above ambient temperatures. Temperatures as of copper from other sources is effected. Arsenates, high as 90 to 95 degrees C. have been used satisfactorily, such as ferric arsenate are preferably added to the ar but routine production is preferably maintained at about 25 senic trioxide reaction stage. 70 degrees C. It has been found advantageous to conduct both of While it has been commonly believed that higher these reactions in a closed, mildly pressurized vessel concentrations of arsenic trioxide may be dissolved which serves to prevent the loss of ammonia and speeds with higher ammonia concentration of the aqueous up the process because of the higher solubility of the solution, this has been found to be untrue. The ammonia 30 oxygen. To keep equipment costs low, the preferred concentration as NH3 should be from about 3 to about 6 pressure is on the order of about 20 psig. The oxygen is percent, optimally around 4%. The ammonia concen avidly absorbed by the reaction and the method by tration may vary between 1 and 12%, but for routine which it is added is not vital. An in-line eductor is suit work, the optimun concentration is best. able for this purpose. Crude arsenic trioxide and even many purified forms 35 During our first year of pilot plant research, on nu of arsenic trioxide are somewhat hydrophobic and tend merous occasions there were slight bits of copper metal to form a separate solid phase above the liquid, thus or cuprous oxide in the final copper arsenate precipi greatly slowing the reaction. We have now found that tate. These are deleterious in that in either form they the addition of a small amount of a low-foaming, non serve to reduce the chromic acid content of the CCA, ionic surfactant, such as Triton DF-16, manufactured therefore requiring either additional chromic acid to be by Rohm and Haas, of Philadelphia, Pa., greatly speeds added or, in many cases, premature precipitation of the up the process. Usually about 1 fluid ounce of surfactant wood preservative. After a great deal of work, we per 1,000 gallons of aqueous ammonia is sufficient for found that the answer was strong dissemination of the effective dissolution of arsenic trioxide. solid copper phase at this stage into the copper The aqueous ammonia solution is capable of ap 45 ammonia-arsenic-oxygen solution. Depending on the proaching quantitative solubilization of any arsenic form, size and shape of the copper or copper bearing trioxide present as such in the incoming arsenic trioxide raw materials used, there should be sufficient agitation bearing raw materials. to suspend these materials throughout the solution until Depending o the nature and quantity of the impurities they have been completely and quantitatively reacted. in the crude arsenic trioxide, it can be desirable to have SO To prevent ammonia losses, the preferred order of more than one annonia reaction or washing step to introducing the reactants into the oxidation vessel is: recover additional arsenic values. Add the copper raw material, preferably in the form For the purpose of describing the steps of the in of a solid or slurry, to the heel of cupric ammonium vented process, it is assumed that this is one of the crude arsenate remaining from the previous reaction. The heel arsenic trioxides that does not require an additional 55 should be about 1% of the volume of the total charge reaction, washing, or filtration step. added. The catalyst should also be added at this time. After the crude arsenic trioxide has been dissolved in Close the oxidation vessel and add the ammonium the ammonia solution to form soluble ammonium arsen arsenite solution. Anhydrous or recovered aqueous ite, the impurities associated with the arsenic, such as ammonia must be added at this point if analysis indicates iron oxide, rock dust, etc., are easily removed by filtra 60 that there is insufficient ammonia to secure the proper tion. If needed, the filter cake, of course, can be washed mol ratio of copper to ammonia to form the oupram or re-pulped and washed or even additionally reacted if monia oomplex (Cu:4NH3). that is the particular nature of this particular arsenic The vessel is then heated to 185 degrees F. temperature, bearing source. and the stream of oxygen is started. Oxidation is rapid In the second reaction step, the ammonium arsenite 65 and exothermic. No additional heating is necessary after solution resulting from the first step is used to dissolve the introduction of the oxygen. The end point of the copper in the presence of cupric ion and oxygen to reaction is determined by: produce cuprammonium arsenite. A third reaction con a: Oxygen reaction stops. Oxygen pressure rises. 5,026,530 5 6 b. Tests for cuprous ion negative. Tests for arsenite SUMMARY OF THE ACHIEVEMENT OF THE ion negative. OBJECTS OF THE INVENTION c. Weight ratio: CuO/As2O5/NH3=1:0.909:1. This ratio is very important. For best results, the copper From the foregoing, it is readily apparent that we 5 have invented an improved method for improving the oxide/arsenic pentoxide ratio must be held as close as environmental and economic quality of CCA, by pro possible to that given. ducing a high purity copper arsenate. This product will After the reaction is completed, any non-reacted free CCA manufacturers from their present dependence matter, such as metallic iron or other impurities intro on a limited number of suitable purity copper and ar duced with the copper source, is removed by settling or 10 senic sources, will significantly lower the cost of both filtration. It is essential that adequate solid-liquid separa copper and arsenic raw materials, will allow the use of tion be used to prevent any metallic particles from pass very impure arsenic raw materials, such as those pres ing through into the copper arsenate. The resulting ently being wasted and stored underground by gold and cuprammonium arsenate solution is now ready for pre copper refiners. The process also allows the use of off cipitation by removing the ammonia. 15 grade copper sources, not only copper scrap, but also In the precipitation reaction, the ammonia can be copper associated with iron by-products and scrap removed from the cuprammonium arsenate by a num products which sell for significant discounts below ber of means, such as inert gas stripping, steam injec copper scrap prices, as well as many copper and arsenic tion, vacuum extraction, heating, or a combination containing by-products from industrial and mining op 20 erations without the need for purification before using thereof. However, to prevent atmospheric pollution, them. The process inherently does not pollute the atmo we elect to remove the ammonia by heating, collecting sphere, and by use of high purity raw materials, the it in scrubbing devices downstream from the precipita process can be made totally non-polluting to the envi tors. Heating is continued until there is no blue color Onment. (the characteristic color of the cuprammonium ions is 25 It is to be understood that the foregoing description blue) in the supernatant liquor. Here again we found and specific embodiments are merely illustrative of the great difficulty in our initial pilot work. About one best mode of the invention and the principles thereof, third of the time, the copper arsenate would not precipi and that various modifications and additions may be tate as anticipated by theory. It forms a gel-like mass made to the apparatus by those skilled in the art, with around the agitator blades in the stripping reactor, caus 30 out departing from the spirit and scope of this invention, ing severe vibrations and the need to heat for days which is therefore understood to be limited only by the rather than hours. Through a great deal of trial and scope of the appended claims. error work, it was found that there was a very narrow What is claimed is: range of copper oxide (CuO) to arsenic pentoxide (As 1. A process for the production of copper arsenate 2O5) ratio that is required to effect rapid, repetitive 35 comprising: precipitation of the copper arsenate. The ratio that is a) reacting arsenic trioxide with aqueous ammonia to produce ammonium arsenite solution, needed for trouble-free production is CuO:As b) reacting ammonium arsenite solution so produced 2O5= 1.0:0.92. Deviation from this ratio of approxi with copper and oxygen in the presence of cupric mately -0.2 is acceptable, but deviation from the opti ion and a halide catalyst to produce cuprammo mum ratio will cause an increase in precipitation time, nium arsenate solution, and and deviation outside the broad ratio range may result c) removing ammonia from the cuprammonium arse in complete stoppage of production. Just before the nate solution so produced to yield a slurry of cop precipitation step, the total concentration of ammonia, per arsenate. copper as oxide, and arsenic as pentoxide varies with 45 2. A process according to claim 1 wherein the arsenic temperature, but usually is just under twenty percent. trioxide is crude arsenic trioxide. The copper arsenate which results from the precipita 3. A process according to claim 1 wherein the arsenic tion reaction can be recovered by many means such as trioxide is in crude form derived from metal arsenides filtration, centrifuging or settling. The copper arsenate Or arsenates. slurry, after filtering, can be used directly in the manu 50 4. A process according to claim 1, further comprising facture of CCA, or the product can be dried for ship beginning with a starting solution of a cupric ammo ping or storage. nium arsenate heel from a preceeding batch, said heel Although the three reactions can be conducted as being about 1% by volume of the total solution. separate stages, this is not necessary, nor indeed desir 5. A process according to claim 1 further comprising 55 agitating said reactants in step "b' to a sufficient degree able. It is also possible, if high purity materials are used, to suspend the copper metal particles or other solid such as arsenic trioxide and copper, to conduct all of copper forms. these reactions in one vessel, including the precipitation 6. A process according to claim 1 further comprising reaction. adding a non-foaming, non-ionic surfactant, in step "a'. The removed ammonia from the process is recycled 60 7. A process according to claim 1 in which removal and used in the following batch operation in the form of of ammonia and resultant precipitation is performed at a aqueous ammonia. copper (II) oxide to arsenic pentoxide ratio of from The process may be operated without solid waste 1.0:0.72 to 1.0:1.12. discharge. This requires the use of sufficient high purity 8. A process according to claim 7 in which removal copper and arsenic raw materials so that no solid waste 65 of ammonia and resultant precipitation is performed at a is generated that might require disposal. This zero solids copper (II) oxide to arsenic pentoxide ratio of 1.0:0.92. discharge process for the production of copper arsenate 9. A process according to claim 1 wherein the copper avoids both atmospheric and environmental pollution. source is selected from group consisting of primary 5,026,530 7 8 copper, scrap copper, cement copper, and bi-metallic 18. A process according to claim 16 wherein the scrap. aqueous ammonia concentration is about 4 percent. 19. A process according to claim 1 wherein the cata 10. A process according to claim 1 wherein the cop lyst is an iodide, bromide, or chloride. per source is selected from copper-arsenic by-products. 20. A process according to claim 19 wherein the 11. A process according to claim 1 wherein the ar catalyst is potassium iodide. senic source is selected from arsenic waste products. 21. A process according to claim 10 wherein said 12. A process according to claim 1 wherein the reac copper-arsenic by-products are copper arsenide and tions are carried out at a pressure above atmospheric. copper arsenate. 13. A process according to claim 1 further comprising O 22. A process according to claim 11 wherein said filtering the ammonium arsenite solution to remove arsenic waste products are selected from the group insoluble impurities. consisting of ferric arsenate, copper arsenate, and cal 14. A process according to claim 1 further comprising cium arsenate. filtering the cuprammonium arsenate solution to re 23. A process according to claim 1, further compris 15 ing recycling the removed ammonia to step a) to con move insoluble impurities. tinue the process, whereby the process results in no 15. A process according to claim 1 wherein step "b' discharge to the atmosphere. - is carried out at a temperature from ambient to about 95 24. A process according to claim 1, wherein said degrees C. arsenic trioxide is purified arsenic trioxide, and further 16. A process according to claim 1 wherein the aque 20 comprising recycling the removed ammonia to step a) ous ammonia concentration is from on to 12 percent. to continue the process, whereby the process results in 17. A process according to claim 16 wherein the no solid waste discharge. aqueous ammonia concentration is from 3 to 6 percent. r K sk sk s 25

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65 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION

PATENT NO. : 5,026,530.

DATED : June 25, 1991 NVENTOR(S) : William F. Drinkard, Jr. Hans J. Woerner it is certified that error appears in the above-indentified patent and that said Letters Patent is hereby Corrected as shown below:

Column 3, Line 49, change "Depending o' to -- Depending on --.

Column 7, Line 21, in claim 16, change "from on" to -- from one --.

Signed and Sealed this Eighteenth Day of October, 1994 Attest: (a (eam

BRUCELEHMAN

Attesting Officer Commissioner of Patents and Trademarks