Counter Current Decantation

Counter Current Decantation

1. Lebong Tandai - Indonesia

My greatest wish in the early years was to secure an order for a CCD circuit. Successful pilot testwork was done in December 1984 at Roxby Downs (see below) where the 1 metre unit was incorporated into a CCD circuit so I was confident it could be done. In May 1986 I attended the Institute of Mining & Metallurgy Conference in Singapore. There I made contact with metallurgists from the Indonesian company PT Lusang who were re-developing a gold mine at Lebong Tandai in Sumatra. It had been worked by the Dutch years before but they had left behind gold bearing tailings which presented an ideal CCD leaching situation. However, as I was to find out on my site visits, the mine location was unique being in a river gorge with steeply sloping sides. There was insufficient level ground to accommodate large diameter conventional thickeners. Their preferred treatment method when I made contact was a horizontal belt filter with counter current washing. I managed to convince them Supaflo thickeners could do the job and would require much less level ground than conventionals.

I returned to Sydney on 17/5/86 and took the first available flight to Jakarta on 25/5/86 taking with me the 100mm test unit. The journey to Lebong Tandai is an all day adventure. First a flight, then a drive over very rough road followed by a 2 hour ride up river in a canoe with an outboard motor before a final hour on a narrow gauge railway. The tests were successful and I returned via the same lengthy route and back home on 31/5/86.

100mm test unit being loaded aboard river canoe

After a lengthy meeting with PT Lusang personnel I finally convinced them and got an order for 4 x 5.5m Supaflos. However supply had to be on the basis of local tank fabrication to our drawings with rakes, feedwells and drives supplied from Australia. Whilst I didn't like this scenario it was necessary to get around Indonesian local content rules for steel imports.

They were in a big hurry to get the plant operating and supply had to be quick. The units were erected and ready to go by November 1986. I spent 3 weeks at Lebong Tandai from 18/11/86 to 6/12/86 supervising final erection details and commissioning the units. We had also supplied, for the first time, closed loop control systems whereby underflow withdrawal rates were controlled by the rake torque and floc dosing rates by the bed level detector.

Placating the Gods.

An interesting sideline occurred prior to the commencement of commissioning. The local people insisted that the plant would not work unless the Gods were placated. To do this they slaughtered a steer and buried its head in the middle of the site. It must have worked because the commissioning went very well thereafter.

I should also mention they roasted its body on a spit and had a grand barbecue. During the following months the operators were able to considerably increase throughput. Mine personnel were delighted with the success of the installation.

Supaflo CCD Circuit at Lebong Tandai http://www.supaflo.com/