Technological advancement in large scale mining has changed little in the past 20 years. Increasing global energy demands and continuously decreasing ore grades are putting pressure on the mining industry to develop new, energy efficient technologies. Comminution has the highest energy consumption across the mining industry, and its energy demands continue to increase as finer grinding is required to liberate the valuable minerals in lower grade ores.
Novel devices, such as high voltage pulse devices (HVP), have the potential to reduce the overall energy consumption, as they offer preferential breakage at the mineral grain boundaries. Good liberation occurs in coarser products and gangue can be removed upstream. HVP devices offer the opportunity to replace and change old inefficient comminution circuits or to be strategically incorporated within a current circuit. They also provide an opportunity for improving the downstream separation performances. However, to date, little research has been conducted on the direct effects of HVP treatment on these mineral separation processes.
In this thesis the effects of HVP treatment on the characteristics and surface chemistry of a sample of Los Bronces porphyry copper ore were initially investigated to determine the potential for improved separation performance. A commercially available SELFRAG Lab device was used to HVP treat the ore either in batch-mode or using the single-particle/single pulse (SP/SP) method. The results showed that the ore responded well to SELFRAG batch treatment, with improvements seen in the ore’s resistance to breakage and mineral liberation. Batch flotation and Wilfley shaking table tests therefore followed, using SELFRAG batch treated and mechanically crushed ore, to determine the differences in the grade-recovery curves. Further froth flotation tests were done using SELFRAG SP/SP treated ore for comparison.
Results indicate that SELFRAG batch treatment of Los Bronces ore significantly reduced the ore’s resistance to breakage when compared to conventional (mechanical) crushing. However, it consumed 21.8 kWh/t whereas mechanical crushing only consumed 1.5 kWh/t to produce the same extent of breakage. The SELFRAG SP/SP method was developed to reduce the consumed energy so that overall energy savings could be realised. In this method, SELFRAG treatment pre-weakens the particles with little to no breakage, so the JKRBT was used to break the particles to -3.35 mm. This method consumed 4.55 kWh/t and the product had the same resistance to breakage as the mechanically crushed product.
Mineral liberation results showed that chalcopyrite was more liberated in the SELFRAG batch treated product than in the mechanically crushed product, noticeably in the coarser size fractions. This was confirmed in the preliminary float/sink gravity separation results where improved chalcopyrite recoveries were seen. Although SELFRAG batch treatment improved the valuable mineral liberation, it also led to noticeable surface chemistry changes. The surface chemistry of pure chalcopyrite was investigated, using X-ray photoelectron spectroscopy (XPS). The high resolution results showed that both SELFRAG SP/SP treatment and mechanical crushing led to the iron oxidising preferentially, leaving behind a copper sulphide passivating layer. However, the SELFRAG SP/SP treatment caused significantly more iron oxidation and the copper sulphides were further oxidised. Separation processes directly after HVP treatment may be inhibited by the degree of oxidation and an attrition stage may be necessary to remove the passivating layer.
Froth flotation tests were conducted at three P80 values, 0.100, 0.150 and 0.200 mm, with the grade-recovery curves showing improved flotation performances after hybrid SELFRAG batch treatment. This was due to the improved mineral liberation and the rod mill ‘cleaning’ the oxidised surfaces. Hybrid SELFRAG single-particle/single-pulse (SP/SP) tests showed improvements in the grades and the recoveries of chalcopyrite for the 0.100 and 0.150 mm samples, but improvements were not seen in the 0.200 mm sample.
The grade-recovery curve obtained from the shaking table results after SELFRAG batch treatment of the ore was better than that obtained after the ore was mechanically crushed. However, the improvement could only be attributed to the grade difference of Concentrate 1 and no conclusions could be drawn on the effects of SELFRAG batch treatment on shaking table separation performance.
A review of the implications on the current mineral processing plant has shown that gangue removal with SELFRAG batch treatment is possible and that improved floatation separation grades and recoveries would be realised. However, the continuous SELFRAG devices used in the mining field merely pre-weaken the ore as in SELFRAG SP/SP treatment. In this thesis the overall specific energy of SELFRAG batch treatment followed by rod milling was considerably higher than conventional mechanical comminution. To produce a P80 of 0.150 mm, 32.5 and 15.7 kWh/t were consumed, respectively. As expected SELFRAG SP/SP used significantly less energy, 18.9 kWh/t, than SELFRAG batch treatment to produce the same size product but it was still higher than that of the mechanical comminution. It was argued that the continuous SELFRAG devices currently available are more energy efficient than the SELFRAG Lab device which was used, and therefore pre-treatment using continuous SELFRAG devices is expected to reduce the energy consumption whilst improving the flotation separation performance.