DRDGOLD temporarily suspends new flotation and fine-grind (FFG) circuits
04 April 2014
DRDGOLD announced today that it has temporarily suspended its recently constructed high grade section – a flotation circuit, a set of fine-grind mills and the cyanide leach and carbon in pulp (CIP) circuit – to determine the cause of the metallurgical problems that have led to lower than expected gold production for Q3 FY14.
Although the new FFG technology, introduced to liberate more gold and increase recoveries by between 16% to 20%, has achieved positive float and grinding results, the CIP section has not yet stabilised and appears to have also contributed to metallurgical instability and carbon inefficiencies downstream in the existing carbon in leach (CIL) circuit or low grade section.
Suspending the new section will enable the operational team to stabilise the low grade circuit and to determine the factors that could be affecting carbon efficiencies in both circuits. The company expects the original lower-grade CIL circuit to be settled within a month. The subsequent test work is likely to be completed within a further three to four month period.
Incessant rains during February and March and surges, dips and interruptions in the power supply during this period have also negatively impacted both the high grade and low grade sections, contributing to the metallurgical instability of both sections.
The Ergo team will therefore make use of the down-time to install drain valves to prevent silting up of the float cells during future power fluctuations, and auxiliary power units to thickener underflow pumps to prevent silting up of thickeners during these trip-outs.
The FFG and high grade CIP circuit came into full operation in mid-January 2014 following the commissioning of a third thickener. Initial results were positive and utilisation was generally good. Flotation efficiencies and the performance of the fine-grind mills were consistent with targets. Sampling results show that the amount of gold remaining in solids (the so-called “washed residue grade”) reduced to within target range. This suggested the gold that previously remained inert within the pyrites was now driven off and had become soluble.
However, loaded carbon values remained well below the target range in both the CIP and CIL circuits. This indicated that the gold remained in solutionand was not being adsorbed onto carbon. To some extent this may be attributable to poor carbon efficiency –caused by volatile density levels in the feed at various stages in the process – which in turn is attributed to the thickeners that manage the flow of feed into the main CIL section. It may also be a knock-on effect of the reagents used in the flotation cells.
Currently both carbon circuits of the plant – the higher grade CIP and the lower grade CIL – are unstable and are operating well below target range.
As a result of these metallurgical inefficiencies and the resultant high dissolved gold losses, gold production for the quarter ended March 2014 is estimated to be 14% lower compared to the preceding quarter, and all-in sustaining unit costs are estimated to be up by 24% quarter on quarter.
Because of a higher gold price and lower total operational and capital expenditure, the company’s cash balance remained virtually unchanged quarter on quarter.
A basic summary of the FFG process and its interaction with the low grade CIL circuit is provided for reference:
Slurry is sourced from various reclamation sites and is delivered to Ergo’s Brakpan plant. The slurry, or feed, is pumped through three banks of flotation cells to create a concentrate that contains gold-bearing pyrites. The concentrate enters a set of fine-grind mills to break down the pyrites and release gold which would otherwise have remained shielded from the subsequent metallurgical extraction process. (Gold trapped in these pyrites is the main target of the FFG and the reason for its construction.) This fine pulp then enters a high grade leach circuit, where cyanide is added to dissolve the gold in the pulp. The concentrate is then pumped to the CIP section where activated carbon is added and the dissolved goldis adsorbed. This loaded carbon is processed through an elution circuit, where the goldis strippedoff the carbon into solution. This solution then flows through a series of electro-winning cellswhere the gold is electrically deposited onto electrodes. Periodically the gold is washed off the electrodes, calcined and smelted into doré bars.
The remaining 96% of the feed leaves the flotation circuit and enters the low grade circuit. It first enters a set ofthree thickeners to increase its density before being pumped into the main CIL tanks. It is essential that the thickeners are in good working order and stable, because the high grade tail cannot be processed by the low grade circuit until it has been thickened. Their purpose is therefore to increase the density of the feed, otherwise the carbon that is introduced later in the process will sink to the bottom of the CIL tanks, and not remain in suspension. From this point onwards in the low grade CIL circuit, the feed is subjected to a similar process to the one described above – cyanidation, carbon loading, elution, electro-wining and finally smelting into dorébars.
South Africa & North America
James Duncan, Russell and Associates
+27 11 880 3924 (office)
+27 (0) 79 336 4010 (mobile)
Investor and Media Relations
Phil Dexter, St James’s Corporate Services
+44 (0) 20 7796 8644 (office)
+44 (0) 779 863 4398 (mobile)
For more information, please visit www.drdgold.com
Many factors could cause the actual results, performance or achievements to be materially different from any future results, performance or achievements that may be expressed or implied by such forward-looking statements, including, among others, adverse changes or uncertainties in general economic conditions in the markets we serve, a drop in the gold price, a sustained strengthening of the Rand against the Dollar, regulatory developments adverse to DRDGOLD or difficulties in maintaining necessary licenses or other governmental approvals, changes in DRDGOLD’s competitive position, changes in business strategy, any major disruption in production at key facilities or adverse changes in foreign exchange rates and various other factors. These risks include, without limitation, those described in the section entitled “Risk Factors” included in our annual report for the fiscal year ended 30 June 2013, which we filed with the United States Securities and Exchange Commission on 25 October 2013 on Form 20-F. You should not place undue reliance on these forward-looking statements, which speak only as of the date thereof. We do not undertake any obligation to publicly update or revise these forward-looking statements to reflect events or circumstances after the date of this report or to the occurrence of unanticipated events. Any forward-looking statement included in this report have not been reviewed and reported on by DRDGOLD’s auditors.