INTRODUCTION

Hydrogen peroxide and its analogues have been used in a variety of processing options for uranium for many years including acid and alkaline leaching as well as precipitation (both direct and from SX strip).

Developments during the late 70’s, early 80’s showed the viability of Caro’s acid as an alternative leach oxidant to the traditionally applied pyrolusite or chlorate for acid leaching uranium ores .

ACID LEACHING APPLICATIONS

Peroxygens are highly reactive in nature and as such have the disadvantage of potentially increasing the consumption of these reagents when used in environments hostile to their stability. Use of Caro’s acid maximises the stability of their oxidation capacity in acid slurry environments. This reactive nature also provides the leach circuit with very rapid response times with respect to ORP control.  Perturbations in leach characteristics such as throughput, head grade and mineralisation variation can be effectively managed quickly.

In the leaching of uranium where ferric ion is the active component, hydrogen peroxide or Caro’s acid can be used to oxidise the ferrous ion back to ferric.

HYDROGEN PEROXIDE AND URANIUM PRECIPITATION

Traditionally hydrogen peroxide precipitation of uranium has been undertaken where interference with impurities like molybdenum, zirconium or vanadium can occur, resulting in the contamination of the final product. Here, the peroxide provides a product free of contamination of these metals, by forming soluble peroxy species with the metal whilst also precipitating the uranium under acid conditions.

There are two potential options for using H2O2 for producing an acceptable uranium product. One via direct precipitation from pregnant liquor, the other from SX strip liquor. In both cases the initial precipitant is uranium peroxide or UO4. xH2O. This material can be marketed as such or further processed to produce U3O8, which is considered to be the more conventional product.

The production of uranium peroxide follows the reaction:

Precipitation by hydrogen peroxide occurs at acid pH’s and is acid generating by nature. pH control is an essential aspect of the process amongst other parameters such as impurity, anion type and uranium concentration.

Direct Precipitation:

In this case, there is a requirement for pregnant liquor uranium concentrations to be high to ensure high efficiencies in both reagent consumption and precipitation. The advantage of the direct approach is to remove the requirement for solvent extraction from processing with a view to reducing both capital and operating costs for the mill.

SX Strip Liquor Precipitation:

Strip liquors from SX are produced by treating the loaded organic with acid or ammonium sulphate (ammonia precipitation route).  For peroxide precipitation route, it is common to use acid stripping of the organic. The principles behind the precipitation process are as for the direct method.  Peroxide precipitation results in a final product with better characteristics in comparison with ammonia precipitation.

Final product characteristics

The nature of uranium peroxide UO4 is such that it is easy to handle (e.g. thickening and dewatering). A comparison of uranium peroxide and ammonium diuranate assay is shown below. In addition to a higher purity, equipment involved can be smaller and more efficient in producing a higher solids density feed stream to a calciner or drier.  The requirement to calcine the final product becomes debatable as UO4 is an acceptable feed stock for uranium enrichment, subject to purity requirements   Elimination of calcining has numerous advantages including energy savings, maintenance as well as reduced capital cost for a drier instead of a calciner.

COMPARISON OF YELLOW CAKE  ASSAYS
(Typical Ranges)

Drying Temperature: 150 - 170^oC