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United States Patent (19) (11) 4,358,430 Victorovich Et Al

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United States Patent (19) (11) 4,358,430 Victorovich Et Al United States Patent (19) (11) 4,358,430 Victorovich et al. 45) Nov. 9, 1982 (54 PROCESS FORTREATMENT OF Refining Slimes” in J. of Metals, No. 5, pp. 764-777 SELENUM-BEARNG MATER ALS (1950). 75) Inventors: Grigori S. Victorovich, Mississauga, D. M. Chizhikov et al., "Selenium and Selenides', Col Canada; Ramamritham Sridhar, let's (Publishers) Ltd., London and Wellingborough, Madras, India; Malcolm C. E. Bell, pp. 57-115 (1968). Oakville, Canada A. A. Kudryavtsev, "The Chemistry and Technology of Selenium and Tellurium', Collet's (Publishers) Ltd., 73) Assignee: Inco Limited, Toronto, Canada London and Wellingborough, pp. 189-205 (1974). 21 Appl. No.: 311,164 R. A. Zingaro et al. (Ed.), "Selenium'', Van Nostrand Reinhold Company, pp. 31-60 (1974). 22 Filed: Oct. 14, 1981 W. J. Mead (Ed.), "The Encyclopedia of Chemical Pro cess Equipment', Reinhold Publishing Company, pp. Related U.S. Application Data 48-49 (1964). - 63 Continuation of Ser. No. 151,349, May 19, 1980, aban O. S. North, "Mineral Exploration, Mining, and Process doned. ing Patents, 1970', p. 184 (abst. of Russian Pat. No. (30) Foreign Application Priority Data 225,448). Chem. Abst, vol. 31, 32226 (1937). Jun. 14, 1979 CA) Canada ................................... 329749 Chem. Abst, vol. 29, 37921 (1935). 51 Int. Cl. ............................................. CO1B 19/00 H. B. Ries, "Granulaterzeugung in Mischgranulatoren 52 U.S. C. ........................................ 423/508; 7.5/99; und Granuliertellern', Aufbereitungs Technik, No. 12, 75/3; 23/313 FB pp. 639-646 (1975). 58 Field of Search ............... 75/3,99; 423/508, 509, R. K. Monahan and F. Loewen, "Treatment of Anode 423/510; 23/313 P, 313 FB Slimes at the Inco Copper Refinery', presentation at (56) References Cited the 1972 Annual Conference of the CIM, Aug. 27-30, U.S. PATENT DOCUMENTS 1972, Halifax, Canada. 2,048,563 7/1936 Poland ................................ 423/510 Primary Examiner-Brian E. Hearn 2,378,824 6/1945 Betterton et al. ................... 423/510 Attorney, Agent, or Firm-Miriam W. Leff; Raymond J. 2,592,421 4/1952 Heilmann .................................. 75/3 Kenny 2,948,591 8/1960 Handwerk .......................... 423/509 2,981,603 4/1961 Tuwiner .............................. 423/510 (57) ABSTRACT 3,231,413 1/1966 Berquin ...... ... 23/313 FB Selenium-bearing materials are treated to convert sele 3,533,829 10/1970 Quanquin ... ... 23/313 FB nium values to water-soluble form in a process which 3,627,486 12/1971 Nakano ............................... 423/509 comprises producing a wet pellet product of uniform 3,816,074 7/1974 Low .......................................... .75/3 composition having a specified moisture content and 4,094,668 6/1978 Yannopoulos et al.................. 75/99 size from an aqueous slurry containing the selenium FOREIGN PATENT DOCUMENTS bearing material and dissolved sodium carbonate-con 1243101 6/1967 Fed. Rep. of Germany ...... 423/510 taining reagent. In a preferred embodiment the slurry is 1176661 1/1970 United Kingdom................ 423/509 pH-adjusted to neutralize free acid and/or to precipitate nonferrous base metals. OTHER PUBLICATIONS J. H. Schloen et al., "Treatment of Electrolytic Copper 25 Claims, No Drawings 4,358,430 1. 2 example, disclose processes in which agglomerates are PROCESS FOR TREATMENT OF formed of the anode slines and soda ash. However, the SELENIUM-BEARING MATERIALSsp methods of these patents have shortcomings, particu larly for anode slimes which have been decopperized by This is a continuation of application Ser. No. 151,349 5 treatment in a strong solution of sulfuric acid. The pro filed May 19, 1980, abandoned. cesses of both patents involve forming mixtures of a This invention relates to a process for treating seleni pasty consistency out of which agglomerates are um-bearing materials. More particularly it concerns an formed. This technique is suitable for processing dry improved method of treating anode slimes with soda materials and not applicable for treating wet selenium ash to convert selenium values in the slimes to a water 10 bearing material containing sulfuric acid. Also the pro soluble form. cesses proposed by the two patents do not apply to materials in which the selenium is present mainly as BACKGROUND OF THE INVENTION both elemental selenium and silver selenide. Most selenium is obtained commercially from various With respect to the slimes containing sulfuric acid, selenium-bearing materials which are by-products of 15 whatever the amount present, the H2SO4 consumes the other metallurgical or chemical processes. The materi alkali carbonate, e.g. soda ash, which is added. Also, the . als are, for example, slimes, sludges, muds, dust and the soda interacts readily with many other sulfates, particu like in which selenium is concentrated along with other larly sulfates of copper, nickel, iron, cobalt, lead, cal valuable elements such as tellurium, silver, gold and cium, etc. All such reactions lead to conversion of the platinum group metals. The method selected to extract 20 soda into sodium sulfate, which, in turn, is of no use for the selenium from a material will depend on such fac the formation of the water soluble selenium compounds tors as its composition, the form in which the selenium during roasting. In addition, the actual amount of soda is present, availability of reagents, cost, and environ left to react with selenium oxides becomes unknown. mental considerations. Details on many processes now Furthermore, it is impractical to mix the wet selenium in use are given in books such as "Selenium', Ed. by R. 25 bearing slimes containing sulfuric acid with the alkali A. Zingaro, pp. 31-60, (1974) and "Selenium and Sele metal compounds needed for the roasting. Mixing Na2 nides' by D. M. Chizhikov et al. pp. 57-115, (1968), CO3 and/or NaOH with the wet slimes containing "The Chemistry and Technology of Selenium and Tel H2SO4 releases a large amount of heat due to neutraliza lurium' by A. A. Kudryavtsev, pp. 189-205, (1974) and tion of the H2SO4 and, the mixture swells out because of in articles such as "Treatment of Electrolytic Copper 30 CO2 evolution when Na2CO3 is added, or it gets more Refining Slimes", by J. H. Schloen et al, J. of Metals, moist with H2O formed when NaOH is used. Also, the No. 5, pp. 764-777, (1950). mixture sputters, contaminating the surroundings, as a Since the most important source of selenium at the consequence of either the CO2 evolution or steam gen present time is anode slimes from electrolytic copper eration. In either case, the heat of the sulfuric acid neu refining, the present invention will be discussed below 35 tralization is capable of raising the temperature of the with reference to the treatment of anode slimes. The mixture up to the point where elemental selenium oxida principal methods of treating such slimes often include tion becomes possible, i.e. slightly above 200 C. This a preliminary decopperization step. One method for highly exothermal oxidation to SeO2 tends to proceed decopperization, for example, consists of treating the so fast that the heat developed cannot be dissipated slimes with strong sulfuric acid at an elevated tempera readily, and the temperature continues to rise. As a ture. This method gives good copper extraction, de result it is not possible to achieve good mixing and there creases the total amount of material to be treated for is a danger of SeO2 volatilization. selenium extraction, and increases the selenium content. There is also the danger of SeO2 volatilization when The present method is particularly suited to slimes the selenium is present mainly as elemental selenium and which have had an acid pretreatment. It is also particu 45 silver selenide. This is caused by the different conditions larly suitable for treating selenium-bearing material under which the elemental selenium and silver selenide which also contains silver. Thus, the method of the react to form SeO2. It is well known that pure silver present invention is discussed with particular attention selenide is quite resistant to air oxidation up to 400 C. to slimes which have been treated with sulfuric acid and while elemental selenium is oxidized and even can ignite which contain silver. 50 slightly above 200 C. There is no clue in either of the In one of the conventional routes for treating copper aforementioned patents on how to provide for complet refinery slimes, the raw or decopperized slimes are ing all the chemical reactions involved while keeping mixed with soda ash and then roasted in an oxidizing the SeC2 from volatilizig. atmosphere to convert selenium to water-soluble so Furthermore, while pure silver selenide is resistant to dium selenite or selenate, which can then be leached. 55 oxidation below 400 C., at higher temperatures, espe Selenium is recovered from the leach liquor by a num cially at about 500 C., it can readily form silver sele ber of known techniques. It has been recognized that nite, Ag2SeO3, which is known to melt at about 530' C. this route requires a very intimate mixing of the seleni and decompose at 550-700' C. When other compounds um-containing particles with soda ash, a sufficient and are present melting of silver selenite may occur at even continuous supply of oxygen reaching all the particles, lower temperatures, thereby obstructing oxidation. An and careful control of temperature so as to avoid a other cause of disruption in oxygen supply may be the fusion which would prevent oxygen from penetrating larger molar volume of sodium selenite and/or selenate the material. It is also necessary to provide sufficient formed as compared with sodium carbonate consumed. soda to convert all the oxidized selenium to a non Both phenomena become real obstacles to complete valatile, water soluble selenite and/or selenate, so as to 65 oxidation when the selenium-bearing materials have Se prevent selenium oxide volatilization.
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