Mining Weekly

JOHANNESBURG (miningweekly.com) – The introduction of new methods of blasting and smelting have the potential to boost platinum mining significantly, says research commentator Dr R E (Robbie) Robinson.

Robinson tells Mining Weekly Online in the attached video interview that the introduction of selected blast mining (SBM) in platinum mining, as with narrow-reef gold mining, requires negligible change to become operative.

The one-time National Institute for Metallurgy, now Mintek, director says it has the potential to boost the economic viability of narrow-reef platinum mining dramatically in the short term.

SBM involves fracturing rock in such a way that the reef remains intact and only reef is brought to surface; the rest of the non-platinum-bearing rock will remain underground to backfill the stopes.

The current method of blasting, which scatters the finely divided platinum far and wide, lowers the rate of platinum recovery significantly.

“We need to use blasting techniques that shock fracture the rock rather than throw it around in big high energy explosions.

Replacing costly smelting with a hydrometallurgical process – known as the Kell process – is the second change he advocates to boost platinum mining.

This process avoids having to separate the chromite from the platinum and, together with SBM, would offer a rate of platinum recovery of well over 90% instead of the current 65%.

Kell, developed by Keith Liddell, consumes only 14% of the electricity that smelting consumes – 140 kWh of electricity for every ton of concentrate processed compared with 1 000 kWh of electricity for every ton of concentrate smelted.

There is also no milling with Kell, which is said to emits only 440 kg of carbon dioxide (CO₂) for every ton of concentrate treated, compared with the milling and smelting of a ton of concentrate to matte and base metal refining producing 1 400 kg of CO₂/t of concentrate treated.

SHOCK WAVE BLASTING

Shock wave blasting, which involves the use of explosives with high detonation velocity and a sudden evolution of gas, sends shock waves that cause rock fracture and keeps precious-metal reef relatively coherent.

“With shock tube and delayed detonation you can do this blasting very satisfactorily without any difficulty whatsoever, and then the shock wave would be automatically transmitted into the reef

“Any decent manufacturer of detonators and explosives would be able to manage this with ease,” says Robinson, who, after retiring in 1990, formed AC Mining Consulting Services, which worked intensively on SBM.

Robinson believes that SBM can serve as a quick, interim solution ahead of the introduction of AngloGold Ashanti’s so-called South African technology, involving automated raise boring and facilitating narrow-reef mining at ultra depth.

Equipment for AngloGold’s “game-changing” technology, which mines “all of the gold, only the gold, all the time, safely”, is under construction, with the first machines scheduled to become available in the first quarter of 2014.

Figuratively speaking, Robinson is “pretty sure” that SBM could be introduced “tomorrow”.