An analysis of a commercial flotation operation cannot be undertaken without considering the effectiveness and characteristics of the mineral collector. While many operations show satisfactory metallurgical performance, others are characterized by low recoveries of certain metals. Factors such as inadequate liberation, surface oxidation of sulfide minerals, or the adverse or depressing action of some modifying agents, often inhibit high recoveries. Under such conditions, it is the collector which often controls the ultimate metallurgical performance.
Perhaps the best example of the limitations of some collectors is in the by-product recovery of molybdenum from copper ores. Recoveries at many plants have traditionally been low, being ascribed to molybdenite locking with gangue minerals or because of low ore grades. To illustrate the impact of low recoveries, billion of tons of porphyry copper-molybdenum ore were milled in the United States. Of the nearly 88 million pounds of contained molybdenum metal, fully 51%, or about 45 million pounds of molybdenum, were discharged to tailings areas. In today’s metal markets, this translates to a considerable dollar value. A similar situation exists for other metals; copper, nickel, precious metals, etc., although to lesser extents. What is required to increase the recoveries of molybdenum and other metals is a mineral collector with powerful adsorption properties.
We will report on a type of collector which was found to be very efficient for sulfide mineral flotation and, moreover, has resulted in significant increases in recoveries of molybdenum, copper, precious metals, and other metals from numerous ore types.
The Pennwalt Corporation began studies of a newly developed flotation reagent, normal dodecyl mercaptan, as a collector for sulfide minerals. Dodecyl mercaptan, a long-chained collector from the class n-alkyl thiols, is now commercially available from the Pennwalt Corporation under the trade name Pennfloat3. The commercial reagent is a mixture of n-dodecyl mercaptan, the primary constituent, and a water-soluble dispersant.
The object of the research program was to evaluate normal dodecyl mercaptan, in the form of Pennfloat3, as a collector for a variety of base metal and precious metal sulfide ores in direct comparison with other collectors under bench scale conditions. This direct approach was chosen in lieu of more fundamental studies, to offer an early indication of the characteristics of the collector and its potential applicability in commercial flotation operations. Such practical data would be available for more detailed optimization studies at the commercial operation.
The extensive laboratory research investigations showed dodecyl mercaptan (in the form of Pennfloat3) to be a highly effective and versatile collector for sulfide mineral flotation. On copper-molybdenum ores, copper recoveries increased 2 to 10 percentage points; whereas, molybdenum recoveries increased from 5 to over 40 percentage points greater than obtained with traditional collectors. Dosages of the experimental collector were lower than for standard collectors on several ores. The potential for increased operating revenues as a result of dodecyl mercaptan use at large tonnage concentrators would, therefore, be significant.
Dodecyl mercaptan was found to be a powerful collector for molybdenite flotation from primary ores. Very high molybdenite recoveries, in the order of 95%, were readily achieved. The most outstanding effect was that dosages of dodecyl mercaptan were as low as 13 to 27% of that typically required for hydrocarbons. Significant cost advantages for Pennfloat3 may be realized at the concentrators. Additionally, no emulsifying agent was required for dodecyl mercaptan, as is for the hydrocarbons.
On precious metal ores, dodecyl mercaptan resulted in strong flotation of gold values associated with iron sulfides. Gold recoveries increased from about 2 to 4 percentage points over those obtained with xanthate-type promoters. Pennfloat3 was also very effective for flotation of platinum group metals and resulted in an increase of 10 percentage points on one ore over that recovery obtained with the operational collector.
Dodecyl mercaptan was also shown effective for flotation of lead, zinc, and nickel sulfide minerals. Increased recoveries were obtained as well as improved selectivity against iron and misplaced metals flotation on most ores.
In view of the demonstrated potential for improvements in the flotation of base and precious metals, especially for copper and molybdenum at operations in southwestern U.S. the use of dodecyl mercaptan (Pennfloat3) cannot be ignored.
Samples of various ore types designated for study were furnished by commercial operators. A representative sample of mill feed (grinding circuit feed) was obtained. Upon receipt the ore was prepared for test work and head assays examined Initially for confirmation with the operator’s estimated values.
Standard or operational laboratory flotation conditions, furnished by the operators, were used for initial tests on most ores. On some, for which no laboratory information was supplied, bench conditions were designed to simulate typical operating practice.
A requirement was that no modifications would be made to the operators standard conditions, such as fineness of grind, flowsheet, flotation times, and major reagent practice (pH modifiers, depressants, activators, etc.). Occasionally, however, minor changes were made to the reagent scheme to examine other conditions and provide additional data on the collector.
Initial tests on each ore involved control tests to reproduce, as possible, typical results using standard laboratory conditioning and reagents, and to provide data for direct comparison with tests using dodecyl mercaptan (Pennfloat3), The correlation between typical laboratory metallurgical results and control tests results was generally good.
Following control tests, dodecyl mercaptan was evaluated by two general methods; i.e., as a “primary” collector and as an “auxiliary” collector. In the former, dodecyl mercaptan was used in place of the standard collectors; whereas, in the latter, it was used in conjunction with the standard collectors. Various pH values, dosages, and points of addition were examined on each ore. It is noted also that the terms “operational” and “standard” collector are used interchangeably in this paper to denote the collector (s) used at the commercial operation.