Vedanta’s US$400 million Gamsberg zinc project near Aggeneys in the Northern Cape will use process control and metallurgical accounting slurry samplers supplied by global specialists Multotec Process Equipment. The project – now commissioning – is being constructed by ELB Engineering Services.
According to Modisaotsile Nyokong, Multotec Process Equipment’s process engineer, the process control samplers will provide a continuous sample to the online population stability index (PSI) and X-ray fluorescence (XRF) analysers. This will enable real-time results to be generated for management and operators at Gamsberg.
“Our unique single-stage vezin sampler and double-stage ‘Two In One’ metallurgical accounting samplers were supplied for streams ranging from 80 NB to 700 NB inlets, to collect representative final composite sample sizes of less than 20 litres per shift,” says Nyokong.
The Gamsberg mine plans to produce 4 million tonnes of concentrator feed a year from the open-pit mine and an annual 250 000 tonnes of zinc in concentrate.
The process control samplers supplied include gravity (shark fin type) and pressurised (pressure pipe) samplers, with each sampler custom-designed to suit the flow requirements of each analyser. PSI analysers require 100 litres per minute, while XRF analysers need 100 to 300 litres per minute.
Nyokong stresses the importance of best practice metallurgical accounting designs ensuring Theory of Sampling and AMIRA standards are applied and considered when proposing and implementing sampling solutions for customers.
“The metallurgical plant needs to be sure that samples collected from metallurgical accounting samplers are representative of the whole shift operation and are used for accurate metal accounting balances,” he says. “Process control samplers, on the other hand, are vital specimen takers, providing samples that are used for real-time process control purposes.”
Nyokong highlights that both metallurgical accounting and process control slurry samplers are used in commodities including gold, platinum and base metals. The benefit of the total sampling solution supplied by Multotec is to have both a process control sampler and metallurgical accounting sampler in the same stream.
The ‘Two in One’ metallurgical accounting sampler – as the name suggests – comprises two separate sample units in one. The primary and secondary sampler units are integrated into one unit allowing for a plug-and-play solution. The unit can be entirely supported to vertical pipework by its inlet flange in an in-line or tank mount position or in the case of larger units using additional brackets on the side of the housing.
Ease of access is enhanced allowing the primary cutter to be inspected and accessed through a bolted hatch on the top and side of the housing, while the secondary cutters can also be inspected through an inspection cover on the top of the secondary housing.
The primary and secondary drive units are self-contained and situated on the top of the units. The blades of the primary and secondary cutters are easily accessible and replaceable, with some adjustment possible on the primary cutters.
“This design makes for efficient and effective sampling,” says Nyokong. “The slot width of the cutter is three times the nominal particle top-size of the solids with constant cutter travel through the stream.”
Another advantage is that the sampling spoon of the primary unit cuts the full stream of the slurry. The sampled slurry reports to the secondary vezin sampler where four cutters cut the full stream of the primary sample. The primary sample is restricted via a conical insert at the inlet to the vezin sampler to ensure multiple cuts of the primary sample increment are taken.
The primary cutter alternates its parked position between two proximity sensors, while the vezin’s cutters run continually throughout the primary sampling interval to ensure representative sampling. The unit also limits splashing when taking primary cuts, and the hood and cutter assembly are made of durable stainless steel with the drive units being splash-protected and dust-protected.
Nyokong notes that Multotec’s single and double-stage vezin samplers conform to Theory of Sampling and Best Practice Cross-Cut Designs, with features that allow ease of access as the cutter can also be inspected and accessed via a large inspection cover on the top of the housing.
In terms of the process control samplers supplied, Multotec’s gravity shark fin type sampler is designed to take a process control sample from a gravity, or non-pumped, process line or launder. The pressure pipe sampler is used to collect samples from pressurised lines. The gravity sampler uses the well-known technique of sampling via a static cutter and is recommended to improve sample representativity for all gravity line applications.
The pressure pipe sampler is mounted into a Y-section with a carefully designed nozzle inserted into the centre of the process pipe. This nozzle has an outlet which is aligned with the sampler so that a well-mixed sample is always drawn.
Multotec has been supplying sampling solutions to the mining industry locally and abroad for over 30 years, with offerings including single-stage, double-stage and even triple-stage sampling systems.
“Our custom designs allow us to meet the specific demands of customers’ applications while delivering practical engineering solutions and still remaining commercially competitive,” Nyokong concludes.