Extraccion por solventes

Las pruebas de extraccion por solventes se realizaron con la fraction concentrada de los elufdos sulfuricos. Cada experiencia tuvo una duration de 24 horas,

empledndose en ellas 6 m³ de elufdo (2 B.V.).

Como extractante orgunico se empleo una solution de 3% de alamina у 2% de isodecanol en tridecano. Como reextractante se utilizo una solution de sulfato de amonio al 15%. A la soluci6n acuosa de reextraccion se inyecto amonfaco gaseoso para mantener un pH de 4,5 a 5,0.

Las soluciones de avance se envfan a precipitacion у la solution de refino se acondiciona у emplea en la etapa de eluci6n.

CUADRO III. COMPOSICION DE LA TORTA AMARILLA OBTENIDA POR PRECIPITACION DIRECTA DE ELUIDOS

(en %)

He aquf un resumen de las condiciones de explotacion у los resultados promedio obtenidos:

Alamine 336 Isodecanol

Relation O/A en E/S Relation O/A operation E/S Tiempo retention E/S (min) Solution fuerte mg/1 U³0⁸ 2.6. Obtencion de la torta amarilla

La torta amarilla se obtiene por precipitation deelufdos ricos о soluciones de avance de extraction por solventes.

En ambos casos, la precipitation se ha realizado a temperatura ambiente en un decantador de 15 m³, en el que se ha depositado la solution; a esta se ha agregado amoniaco gas hasta alcanzar un pH de 7 a 7,5 agitando simultaneamente mediante inyeccion de aire comprimido.

La concentration en U³0⁸ de la torta amarilla obtenida por precipitation directa de elufdos estd comprendida entre el 12,8 у el 20,6%, mientras que la de los precipitados obtenidos a partir de las soluciones de avance de extraction por solventes ha fluctuado entre el 68 у el 78% de U³0⁸. El sobrenadante de la precipitaci6n contiene de 40 a 68 ppm de U308.

En el Cuadro III se indica la composition de los precipitados obtenidos.

Las pruebas de purification de la torta amarilla obtenida рог precipitation directa de elufdos, realizadas en el laboratorio, han permitido obtener muestras de concentrado de un 84,74% de U308, con contenidos de fierro, cobre у molibdeno del 0,04, 1,0 у 0,78% respectivamente.

3. CONCLUSIONES

Se probo la factibilidad tecnica de recuperar uranio, en forma de torta amarilla, a partir de las soluciones de lixiviacion de cobre de la mina Chuquicamata Sur, sin producir interferencias en el proceso de production de cobre.

Debido a la rdpida declinaci6n de la recuperation en la etapa de carga de intercambio ionico, resulta conveniente trabajar con ciclos de carga cortos. A este respecto, se est£ estudiando a nivel semipiloto el empleo de mas de dos columnas en serie.

Dentro del rango de flujos de soluci6n probados (0,7, 1,4 у 2,1 gal/min/pie²) resulta conveniente trabajar con el flujo mds alto, dado que, sin afectar sensiblemente la recuperaci6n. se logra el mds alto nivel de carga en la resina (3,1 g de U308/1 de resina).

Si bien los concentrados obtenidos en la planta piloto no cumplen las

especificaciones de pureza nuclear, pruebas de laboratorio indican que tecnicamente es posible purificar la torta amarilla hasta alcanzar niveles comerciales.

DISCUSSION

S. SEN: Have you worked out any cost figures for the recovery of uranium -from this dilute solution?

N. ANDALAFT: At present we have only been concerned with the technical details and problems of recovery of the uranium from the solution, so that we do not have figures relating to economics which can be said to have any relation to what might be the final process.

D.W. BOYDELL: First, how much uranium remains in the resin after the elution with NaCl and H²S0⁴? Second, what is the temperature of the sulphuric acid elution? Third, what is the concentration of uranium in the effluent?

N. ANDALAFT: First, although no figures from direct resin analysis are available, owing to the low reliability of such analyses, it can be estimated on the basis of solution balances that approximately 20% of the uranium loaded in the resin remains in it after elution with sodium chloride and between 30 and 50% remains after elution with sulphuric acid.

Second, the elution with sulphuric acid was always carried out at ambient temperature, i.e. between 10 and 20°C.

Third, the uranium concentration in the effluent increases between two successive alkaline washings of the resin. This variation can be seen in the table below, which shows the average uranium content in the effluent for four-day loading operations, between two successive regenerations of the resin.

Effluent

A. HIMSLEY: It is stated that the resin is loaded with between 1.3 and 3.1 g of U308/ltr. If this were completely eluted from the resin by using four bed volumes of the recycling eluant, the result would be an eluate of between 325 and 775 ppm U308.

The figures of 220 to 360 ppm given as the average concentration of the eluate would indicate a removal of only 0.88 to 1.44 g of U308/ltr of resin. If the difference remains in the resin, it could lead to a relatively high concentration of U³0⁸ in the final effluent. Could the author clarify this point?

N. ANDALAFT: As Mr. Himsley implies, it is effectively established in the operation of the pilot plant that the residual uranium content in the effluent is high and that, furthermore, this content increases with successive loadings between resin regenerations. The residual uranium content of the resin and also of the effluents has been indicated in the replies to Dr. Boydell's questions.

F.R. HARTLEY: You mentio that the copper solution contains between 10 and 18 ppm of U308. This would represent a relatively steady state concentration balanced through the whole inventory of the leaching and tank house circuits over a significant period of time. However, would you yet know how much copper is

•entering the circuit from the ore. That is how much will be available for extraction and what concentration the liquor will be once you start recovering the uranium from it?

N. ANDALAFT: It has actually been quite difficult to determine how much new uranium enters the solution from the ore. This is basically due to difficulties in sampling and analysis of the solids. Nevertheless laboratory leaching with recycling has indicated that these levels of uranium content in the solutions would be more or less the steady state level.

A. HIMSLEY: I would like to comment on this. In another similar operation the equilibrium level of uranium in the leach circuit went down to about one third of the previous equilibrium level.

D.W. BOYDELL

South African Atomic Energy Board, Randburg,

South Africa

Abstract

IMPURITIES IN URANIUM PROCESS SOLUTIONS.

Several uranium purification circuits are presented in tabular form together with the average major impurity levels associated with each. The more common unit operations in these circuits, namely strong- and weak-base ion-exchange, solvent extraction and the precipitation of impurities are then discussed individually. Particular attention is paid to the effect and removal of impurities in each of these four unit operations.

1. INTRODUCTION

Uranium purification circuits are as varied as the ore types that are treated for uranium recovery. The major features of the more common circuits that have been employed are shown in Table I. Table II summarizes circuits that have been developed under special circumstances but which will be employed more

frequently as these ore types are increasingly exploited in the future. Reference will be made to these circuits as each unit operation in uranium recovery is reviewed.

The nature of uranium mineralization in an ore will determine the severity of the conditions necessary to render the uranium content soluble. If all or part of the uranium is present in aggregations too small to be exposed directly to the leaching agent it may be necessary to dissolve barren material in order to liberate and dissolve the uranium. Uraninite occluded in pyrite, and uranium atoms contained within the crystal lattice of zircon are examples of occurrences that require severe leaching conditions for uranium dissolution. Similarly, the uranium-containing multiple oxides, brannerite, betafite and pyrochlore, are particularly refractory, and effective leaching conditions will render appreciable quantities of subsidiary minerals and gangue material soluble.

Figure 1 shows the unit operations in uranium ore processing. In general there will be a strong interaction between the process choices made for adjacent unit operations. There will, however, seldom be economic justification at the design stage for moderating the conditions of the leach (with consequent lower uranium extraction) to alleviate problems that may occur in the purification and

29

No.

NOTES: SBIX - strong-base ion-exchange ADU - ammonium diuranate SX - tertiary amine solvent extraction SDU — sodium diuranate WBIX — weak-base ion-exchange

No.

NOTES: TBP - tributyl phosphate solvent extraction UPO — uranium peroxide

ORE

1

SIZE REDUCTION

I

LEACHING S / L SEPARATION

I

I

PURIFICATION AND RECOVERY

I

YELLOW CAKE

FIG.l. Unit operations in uranium ore processing.

recovery sections of a uranium plant. Existing technology may be adapted to treat any solution containing economic concentrations of uranium. In a number of recent uranium plants, however, uranium purification and recovery sections have proved to be a bottleneck to production, necessitating prolonged commissioning periods, loss of revenue and costly modifications.