Experimental Procedure

Lixiviation
The product of the flotation presented the granulometric distribution.

The material was homogenized and quartered in lots of 1 kilogram. A sample considered representative was taken for chemical analysis.

The stage of cyanatation was preceded by a lixiviation with alkalined solution with lime oxide (CaO), of pH 10.7. this value considered optimizing, was maintained during all the cyanatation with periodic addictions of calcium oxide and pulp.

E pH must not be more elevated, due to the fact that the adjoined effect with the ions ca++ and pH over the process is prejudicial and increases with the pH.

The volume of water to be used was examined in volumetric tanks, and in tests with heating the level was completed when it was necessary. The quality of water used is of extreme importance, due to the fact that it can include many strange ions to the process being studied, modifying the results. In the laboratory was distilled water was used. The temperature was examined continuously, being the level inferior of 25°C and the superior of 70°C.

The agitation of the pulp was promoted by a mechanical agitator, being sufficient for maintaining the solids in suspension. The bubbling (air or oxygen) was performed by controlled evacuation, measure in rotameter and of value 2.5 1 min. -1. in almost all the tests, the bubbler was preseen of synthesysed glass which allowed a good distribution of the air in the pulp. Through the test, aliquots of 10 milliliters were removed for an immediate analysis of the tenor of gold by atomic absorption. The remaining volume was replaced in the reactor to avoid too many variations of volume. At the end of the tests one aliquot of 500 ml was removed for an analysis of a higher number of elements. The interval of time between the taken aliquots varied a little in some tests, but generally augmented with the process of the practice (2, 6, 10, 20, 30 hours). The solid residue of the lixiviation was washed with hot alkalined water with hydroxide of sodium (NaOH), and stored for future elimination. All the solution which comes from the lixiviation, including waters of washing was stocked for precipitation of the cyanate in the form of a stable compound Fe4Fe (CN) 6 3, with the intention of avoiding contamination of the effluents in the station of treatment of water.