Merensky and UG2 concentrator plants

Crushing/screening circuit: In the crushing/screening circuit the ore is crushed to reduce its size before it reports into the mill.

Milling: Merensky ore feeds into a fully autogenous mill (FAG mill). In the UG2 plant the crusher product feeds into a high pressure grinding roll crusher (HPGR) and this then goes into a primary ball mill.

Flotation: The circuit includes rougher cells, scavenger cells and cleaner columns. In the UG2 plant the secondary roughers consist of a bank of tank cells.

In the UG2 circuit, sparger columns act as a cleaner and help to produce a final UG2 concentrate at half the original chrome content while maintaining PGM recoveries.

Smelter and furnace operations

Commissioned in 1993, the smelter has a 15MW capacity. Key processes are drying, smelting and converting the concentrate. Concentrates brought in are blended in by a conveyor. Dried concentrate is pulverised and then stored in silos. The off-gases are cleaned in an electrostatic precipitator, where fine concentrates are recovered too.

The concentrate and flue dust are mixed with lime and then feed through to the day bin and into the furnace.

Inside the furnace electrodes provide heat. The lighter oxides float to the top as slag, and the more dense sulphides, which contain the PGMs, sink to the hearth as furnace matte.

The smelter at Zondereinde has for years treated Zondereinde's output and spare capacity has been filled with toll-treated third party concentrate. In line with the company’s expansion and Booysendal operations coming on stream, the smelter is being expanded, and a new furnace is being built to make provision for the higher volumes. Innovative design parameters allow the facility to operate as a pure UG2 furnace, apart from being a conventional smelter also for a combination of Merensky and UG2 concentrate. This new design comfortably accommodates the growth in UG2 mining.

Northam life cycle diagram

Hover over numbered elements for the descriptive process flow
FAG product is pumped to primary cyclone. The underflow feeds a flash flotation cell. The concentrate product reports to the thickener and the tails to the ball mill.
Crushing and screening of UG2 ore.
Merensky ore is crushed and conveyed to a stockpile. The ore is fed via a conveyor to the FAG mill.
The crushed UG2 ore is fed to the HPGR, then into the primary ball mill.
The concentrate reports to the thickener feeding the cleaners. The resulting recleaner concentrate product is fed to the sparger for upgrading before being sent to the thickener.
Concentrate from the cleaner cells reports to the thickeners. Tailings are pumped to the backfill plant. Concentrate is thickened then hauled to the drier at the smelter.
Dried concentrate is pulverised and conveyed to silos. Off-gases are cleaned in a precipitator to recover fine concentrators. The concentrate is mixed with lime and fed through to the day bin. Electrodes heat the furnace which relies on a gravity separation process: the lighter oxides float to the top as slag and the dense sulphides sink to the hearth as furnace matte.
The matte (a combination of iron, nickel and copper sulphides) also contains contaminants in the form or iron and sulphur. PGMs are collected in the copper and nickel sulphides. The matte is poured into the converter and air is blown through tuyeres at the bottom of the converter. The oxygen reacts with the sulphur and iron to produce SO2 which goes into the flue gas system and iron oxides which form converter slag. The slag is skimmed from time to time in order to produce a bath of high grade converter matte. The matte is granulated and pumped to a settling tank where it is dewatered, bagged and transferred to the BMR. The PGM recovery is 98.5%.
Processes in the BMR include atmospheric leaching, pressure acid leaching, selenium removal and copper electrowinning.
Precious metal refining where high purity refined metals (Pt, Pd, Rh, Au, Ag, Ru and Ir) are credited to Northam to be distributed to Northam customers globally.