Патент USA US3044857код для вставки
United States Patent 0 1 ‘ 3,044,849 3,044,849 1 ‘Patented July 17, 1962 2 ing progresses. It has thus become common practice to add more glue during the leaching process so as to bring the total amount between 1.0 and 2.0 lbs./ ton ore, which adds appreciably to the cost of uranium processing in view of the small amount of uranium in each. ton, of. Ore It is the primary object of this invention to overcome ‘ PREVENTION OF SETTLING 0F URANIUM PULP BY POLYVINYL ALCOHOL Frederick W. Matthews and‘ Max Mort, St. Hilaire, Que bec, Canada, assignors' to Canadian Industries Lim ited, Montreal, Quebec, Canada, a, corporation of Canada No Drawing- Filed Sept. 14, 1959, Ser. No. 839,562 Claims priority, application Canada Oct. 11, 1958, 2. Claims. (Cl. 23—14.5) the foregoing disadvantages by providing a new suspend ing agent for the uranium pulp, which agent is more e?ec tive than the animal glue and is also more stable under 10 the leaching conditions. Other objects of the invention This invention relates to the extraction of uranium will appear hereinafter. from its ores and, more particularly, to the prevention of Broadly speaking, these subjects are accomplished by settling of the pulped o're during the leaching thereof. incorporating polyvinyl alcohol with the pulp in. a con Many uranium ores contain the uranium in such forms centration of at least 0.01 pound per ton of uranium ore as uranium titanite, uraninite and pitchblende dispersed 15 contained in the pulp. ‘ ' as ?ne particles through an essentially quartzite matrix. The effectiveness of the polyvinyl alcohol as suspend The amount of U308 mayrange, for example, from 2.0 ing agent does not appear to be dependent to a great ex to 20.0 pounds per ton of ore. To extract the uranium, the ore is ?rst crushed, and then ground under water until about 55% of the ore passes a 200 mesh screen. a tent on its molecular weight or hydroxyl content, having regard to the fact that polyvinyl alcohol is produced by This 20 hydrolysis of polyvinyl acetate. Thus, the following com ?nely divided ore, when slurried in water, is normally mercial grades of polyvinyl alcohol were tested and all found to be effective forthe purpose of the invention. known as uranium pulp, and in the next stage of the proc ess, the pulp is brought to 60%-70% solids and leached with sulphuric acid under oxidizing conditions. It is with 25 this leaching step that this invention is concerned. The leaching is normally done in a wooden stave or rub Viscosity in centipoises of 4% aqueous solution at 20° C. ber lined tank or series of tanks measuring roughly 30 ft. deep by 32 ft. in diameter. The pulp is brought into con tact with sulphuric acid of about 5% strength containing 55-65 a small amount, viz. 2-3 pounds per ton of ore, of so 30 dium chlorate at a temperature of about 45 ° C. The leaching is continued for about 48 hours and the ura nium becomes oxidized to the uranyl state and remains in Degree of Hydrolysis,’ percent 99-100 0 .___ 97'. 9-98. 7 solution, probably as uranyl sulphate. It is vital to the success of the leaching process that the pulp, containing 35 for example 65-68% solids, be kept in motion by con The solid ponyvinyl alcohols of 99-100% degree of hydrolysis and medium or high viscosity ‘dissolve slowly through the pulp. Very large and powerful stirrers are in the leaching solution and it is preferable that they be used, and there has been in the past considerable loss and incorporated with the pulp in the form of aqueous solu 40 damage caused by the tendency of the pulp to settle from tions of any convenient strength, rather than in solid the liquor as a semi-solid mass. Such settling may over form. load the motor or bend the stirrers, and is particularly The invention will be more fully illustrated by the fol likely to occur at any interruption of the electrical power lowing example which, however, its not intended to limit or compressed air supply. Once the pulp has settled and the invention. the damage is done, the tank must be emptied by removal 45 EXAMPLE of all pulp and lengthy and costly mechanical repairs may A simple test was devised for comparing the e?ective follow. Moreover, this tendency to settle increases the ness of various suspending agents. This test consists in power requirements of the stirrer by a large factor. pouring a sample of the pulp containing the leaching In order to decrease the danger of such settling, it has become common practice to incorporate a suspending 50 chemicals and particular suspending agent into a wide bore powder funnel of speci?ed dimensions. The bore agent in the pulp during the leaching procedure, the pre of the funnel is plugged at the bottom with a rubber stop~ ferred agent having heretofore been animal glue. The per and the pulp allowed to settle for 15 minutes. The glue is usually added with the sodium chlorate, since on stopper is then removed and the time for the contents of the initial addition of sulphuric acid to some uranium stant stirring and in some cases by compressed air blown ores there is emission of hydrogen sulphide, i.e. the con 55 the funnel to ?ow out is noted. This time is an excellent measure of the tendency of the pulp to settle, and the ditions are reducing. The pulp is air blown until the size of the funnel and its bore may be varied to measure hydrogen sulphide is drawn off and the sodium chlorate this tendency over several ranges. Thus a pulp which is and glue are then added. Initially about 0.3 lb‘. glue are added per ton of ore. - e?ectively suspended by either glue or polyvinyl alcohol By the term “suspending agen ” as used herein is meant 60 may ?ow out of a given funnel in 5-7 seconds but a pulp an agent which not only slows down the settling of the pulp from the leaching‘liquor but also changes the na ture of the semi-solid‘ mass it it should be allowed to set tle. In the absence of a suspending agent the settled mass is hard like wet sand 'but in the presence of an e?ective agent the mass is much less dense and is capable with no agent or in which the agent has become ineffec tive will not ?ow out of the same funnel at all. Various suspending agents were incorporated with sep arate samples of a uranium pulp containing 68% solids. 65 to which were added 4 cc. of sulphuric acid and 0.5 g. of sodium chlorate per 200 g. of ore. Each sample was stirred and brought to 45° C. and tested by the above of being stirred into suspension again with little elfort. method using a funnel with a 1.3 cm. diameter bore. However, experience has shown that glue is not stable Since high molecular weight glues are more effective under the acid oxidizing conditions prevailing during the 70 than those of low molecular weight, a glue of the former leaching process. Moreover, even in the presence of glue, type was compared with three samples of polyvinyl al the tendency of the pulp to settle increases as the leach cohol with the results shown in Table I. 3,044,849 4 It is permissible to add the polyvinyl alcohol at the be Table l ginning of the leach, and no deleterious effect is occa sioned thereby. Flow-Out Test Time (seconds) Leaching Time (Hours) ‘ ‘ ~ _ 5 alcohol than those above in Table II can be used for Polyvinyl Alcohols particularly difficult ores. It is economically desirable to use the minimum e?ective amount of suspending agent, ‘but the process of this invention is not to be limited to small amounts shown in the example, but only by the Glue 1 7 28 g ' 2 3 between 5 an d 10 ’ ' 10 31 following claims. What we claim is: m m ~ It should be noted that a greater quantity of polyvinyl 15 9 V. 1. In a process wherein ?nely ground uranium ore is 15. 5 slurried with dilute sulphuric acid and leached under oxi dizing conditions, the improvement which comprises in The concentration of glue was 0.3 lb./ton which corre sponds to the ?rst addition in a leaching proceess, while 15 corporating with the slurry at least 0.01 lb. of polyvinyl that of polyvinyl alcohol was only 0.05 pound per ton of alcohol per ton of ore. ore. ‘It can thus be seen that the e?ectiveness of the glue was lost in 6 hours, and therefore more glue must be 2. The improvement claimed in claim 1 wherein a polyvinyl alcohol having a viscosity of at least 25 centi poises in 4% aqueous solution and a degree of hydrolysis of at least 99% is incorporated with the slurry in the added in practice, whereas the polyvinyl alcohol was still e?ective after 48 hours, the usual total leaching time. A similar experiment was conducted to establish the effect of decreasing amounts of polyvinyl alcohol. form of an aqueous solution. In this‘ case the polyvinyl alcohol had a viscosity of 19-25 and a dagree of hydrolysis of 86-89%. The results of the experiment are given in Table II. 25 Table II Concentration of Polyvinyl Alcohol Test Time of Two (lbs/ton of ore) Samples (seconds) 30 10 15 8 16 16 18 55 18 20 63 References Cited in the ?le of this patent UNITED STATES PATENTS 2,738,253 2,868,618 Thunaes et a1. ________ __ Mar. 13, 1956 Oberg et a1. __________ __ Jan. 13, 1959 OTHER REFERENCES Rosenbaum et al.: “Int. Conf. on Peaceful Uses of Atomic Energy," vol. 8, pages 38-44, August 8-20, 1955. Kirk and Othmer: “Encyclopedia of Chemical Tech ' nology,” vol. 14, pages 713, 715.