Following successful trials, commercial manufacture is the next step for new technologies that measure bulk ore’s moisture content on conveyor belts and the particle size of solids in transported mineral slurries.
The low-frequency microwave (LFM) moisture analyzer and the ultrasonic particle size analyzer (UltraPS) provide continuous, real-time data with a high degree of accuracy and reliability, and a minimum of expensive on-site maintenance.
The LFM moisture analyzer uses microwaves to measure the moisture content of minerals such as coal and iron ore, whereas the UltraPS continuously determines particle size using measurements of ultrasonic shrinkage and velocity in the stream.
The moisture and particle analyzers provide data quickly, saving vital time and money. Without online measurement, samples are collected and tested by laboratory analyzers. Results can take several hours, severely limiting the opportunity to control processing operations.
Both units were designed and engineered by the Commonwealth Scientific and Industrial Research Organization (CSIRO) On-line Analysis and Control group. Its design is “ruggedized” for use over wide temperature ranges, and in dusty or high-vibration conditions. An additional feature is built-in modem communications, allowing CSIRO staff to evaluate and fine-tune performance remotely. Mobile phone units can sometimes be used in areas without landlines.
David Miljak, CSIRO Minerals’ moisture analysis expert, says online diagnostics and support are becoming standard practice as phone access to remote areas becomes more reliable.
An automated phone system allows the CSIRO to track the analyzers’ operations over the long term. “To travel to the Pilbara or far-northern Queensland from our base in Sydney for minor problems is inefficient,” says Miljak “So we gain access to the units using phone modems, which lets us look into the analyzer directly and determine if there is a particular problem. The phone links are reliable, so the client does not have to worry. The links allow us to bring a specialized level of support to these systems. We provide maintenance support as well as technical advice and installation, and the client can offload all that on to us.”
Eleven LFM moisture analyzers are now operating in the field in Australia, after BHP Billiton Iron Ore led the way with trials starting in 2002. More will be deployed over the coming year. The moisture analyzer was developed for continuous, on-conveyor applications ranging from conventional materials to highly attenuating materials, such as iron ore, mineral concentrates and high-moisture coals. It can be installed with little or no modification of existing conveyor belts. Once installed and calibrated, the system operates continuously without the need for sampling.
Moisture control is especially necessary in bulk ore-handling operations: too dry, and dust emission can create problems when loading or unloading; too wet in the train leaving the mine, and the ore may become difficult to unload and handle at the shipping port, causing costly delays.
The UltraPS is a new ultrasonic particle size analyzer suitable for a wide range of industrial applications. It operates on high solids content slurries, with a submersible probe inserted into the stream to measure particles over the range 0.1 to 1,000 microns. It has been field-tested successfully, with several commercial prototypes now operating in Australia and South Africa.
Getting the particle size right in a minerals processing plant is critical. The particles need to be ground fine enough that gold, platinum and other precious metals can be separated from the waste rock. “Milling ore can constitute more than sixty per cent of the energy used in mineral processing plants,” says Michael Millen, CSIRO Minerals’ in-stream particle size project leader. “If you over-grind it, that is a huge waste of energy and money.”
If the particle size is wrong, then precious metals can be lost to the waste stream, or waste rock dilutes the purity of the desired concentrate stream.
“Companies want to be able to measure the particle size in real time, so they can work out if they need to grind the ore a bit more or less, and save money,” says Millen. “An on-line analyzer will get the same result as a laboratory analyzer, but in a period of one to two minutes instead of hours.”
Work on developing the UltraPS began in the early 1990s. Other on-line particle size systems have not proved reliable in handling the tough conditions in mining operations, but CSIRO Minerals’ analyzer has proved to be robust. CSIRO Minerals is now working on a multiplexed system so that the analyzer can handle multiple streams.
— The preceding is an edited excerpt from Process, a monthly publication of the Commonwealth Scientific and Industrial Research Organization based in Melbourne, Australia.
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