New technologies for the treatment of uranium ores

The new technologies on hydrometallurgy which are described concern operating conditions of acid leaching, solid liquid separation after leaching, and solvents recuperation of uranium. The acid leaching of the pulp obtained from a humid crushing uses sulfuric acid in variable but always in fairly high quantities. This is being due to the loss of free residual acid at the end of the leaching. Indeed, experience shows that a good yield of uranium solubilisation can generally be obtained if the percentage of free acid remains over a determined level. All experiences done in the world to recover this acid by the means of a methodic leaching at counter-current have failed because of filtration problems. This question can be partly solved, if after dry crushing and preheating of the ore, a leaching by S.A. is done at a suitable concentration in order to obtain a thick middle. This technique has been successfully applied at the Arlit plant, operated since 1971 by SOMAIR in the Niger Republic. This technique will also be applied, with minor differences in the Akouta Plant, also in Niger, which is now under studies for the account of COMINAK. The solid-liquid separation and the washing of the pulp by counter-current methodic circulation in a set of decanters shows several disadvantages. They need large quantities of water. They accordingly give very diluted uranium solutions. But the down stream installations for the uranium recuperation, and mainly solvents installation are larger and consequently as costly to build and to operate as uranium content of solution is low. They take a long time and a lot of difficulties to stop and to restart, they cannot be stopped regularly such as at the end of the week. They give a very liquid cake, which needs, for its storage, a failing disposal with high level of security against any accidental losses of liquid to surrounding waters. These troubles can be avoided by a washing and a separation on filters. This technique, which was very difficult and costly year ago when using rotating filters has been largely improved by the use of horizontal bands filters. In most cases, their use improves greatly the concentration operations. This is an already old process. But in this field, many technologies have been developed for improving efficiency. These improvements, as well as the increase of uranium in influents allow to reduce within a great proportion the cost of investments and of exploitation of such solvents installation. At last, very pure concentrates, especially of ammoniac diuranate, can be obtained by judicious arrangement between means of extraction and reextraction. Consequently, it is possible to consider for UF4 and UF6 plants a ''short way'' more rapid and less expensive than the ordinary way now used