Ultra Hard Coating Extends Pressure-Monitor Diaphragm Life at Xstrata Mill
Xstrata Nickel operates five ore processing lines at its mill in Onaping, Ontario. Each line includes a cyclopack, consisting of a group of hydrocyclones arranged in a circle to share ore separation duty. Nickel ore slurry flows to the top of the cyclopack, where it is distributed to the cyclones.
According to Brian Couling, electrical and instrumentation supervisor at the mill, the nickel ore slurry with 70% solids enters the bottom of the cyclopack through a 14-inch pipeline. “The slurry travels up to the pot head, which distributes the fluid evenly to the circle of cyclones,” says Couling. “We measure the pressure at the top of the pot head,” he says. “At a flow rate of 200 to 400 cubic meters per hour the slurry is literally sandblasting this pressure measuring system.”
Slurry pressure measured at the pot head guides mill operators in turning individual cyclones on or off. If the pressure is too high, they add cyclones to maintain desired pressure values and vice versa.
“In this particular mill we have five cyclopacks monitored by pressure sensors,” said Couling. “The measured pressure range is relatively low, about 7 to 12 psig. So we have a high-flow, low-pressure system of an extremely abrasive slurry.”
The slurry caused serious erosion of metallic diaphragms in the pressure transmitters monitoring the slurry flow—even when retrofitted with a protective rubber pad. Transmitters failed unpredictably and frequently, requiring replacement once or twice a year. Cost to the mill was thousands of dollars per hour in unscheduled downtime, plus costs for transmitter replacements.
Seeking a solution to this ongoing problem, Xstrata accepted a proposal from ABB Instrumentation in Canada to designate the mill as a beta site for trial installation of an ABB pressure transmitter equipped with a diaphragm protected by an innovative coating called Diaflex.
Diaflex, composed of silicon and titanium combined as a nitride, has exceptional resistance to abrasion. ABB coats a 316 stainless steel diaphragm with Diaflex to a thickness of 3 to 5 µm. Diaflex has a hardness similar to that of diamond, but the deposition technology used provides an adequate spring rate value to ensure diaphragm flexing for process temperatures ranging from -100°C to 700°C.
In the trial installation, the mill replaced an existing transmitter with an ABB 264 direct flange-mounted pressure transmitter (2600T series) with a Diaflex-coated diaphragm. For this trial test, no rubber pad was added.
The ABB pressure sensor operated for more than two years with no sign of diaphragm deterioration. As a result Xstrata has converted the other four Cyclopacks to the test-proven ABB pressure transmitter. The mill is also testing Diaflex-coated diaphragms on other transmitter applications.
Dual-Purpose X-ray Analyzer Prototype Replaces Two Separate Systems
Australian scientific organization CSIRO reports that a research team recently had a “light bulb” moment, prompting them to change the course of their study—originally aimed at creating two very different x-ray based slurry analyzers.
Although they had been designing two systems—an x-ray fluorescence (XRF) slurry analyzer for sensitive chemical composition analysis and an x-ray diffraction (XRD) slurry analyzer for more general use—they began to realize there could be value in combining them into a single unit, according to a report in the October 2009 issue of CSIRO’s Process magazine.
The minerals industry has traditionally relied on these two x-ray-based technologies to determine a material’s characteristics: XRD for mineralogy and XRF for chemical composition. But as work progressed, researchers found a growing commonality in their designs.
CSIRO ’s Dr. James Tickner, who heads the team developing the analyzers, said the amalgamation of the XRD and XRF methods came fairly late and was “a big leap for us.”
“Originally, we set out to build separate systems tackling very different problems,” he explained. “Our XRF analyzer is designed to be extremely sensitive for key elements. The XRD analyzer is a more general tool, capable of measuring a wide range of minerals in both slurries and dry powders.”
Essentially, the work has combined the best aspects of XRD and XRF analysis technologies to create a new prototype capable of measuring both mineralogy and ultra-low elemental composition directly on a process-stream without the need for labor-intensive, time-consuming and potentially error-prone sampling.
The spin-off has been a near halving in the tool’s cost and complexity, meaning the new unit is a more compact and cost-effective product. “This is a bonus for us. Our initial focus was to achieve simultaneous mineralogical and elemental analysis in one package.”
The technology, dubbed XRDF for its dual origins, has been designed to operate directly on-stream for plant control and monitoring applications. It measures a material’s characteristics as it passes through the analyzer in the form of a slurry. By using a “launder tank” geometry, a wide range of flow rates up to 100 liters per minute can be accommodated. The analyzer reports updated composition parameters every minute, allowing rapid responses for plant control. The XRDF prototype can be readily adapted to measure different elements and minerals, making it well-suited for a wide range of applications and industries.
The first industrial prototype, currently under development, will undergo an industrial trial in early 2010. “We need to ensure that the instrument is fairly bulletproof for industry applications and that it can survive any rough handling it might receive,” Tickner said.
For elemental analysis, the research team also believes the prototype is 10 times more sensitive than other commercial slurry analyzers. “We can detect down to a level of about 100 parts-per-billion, allowing us to measure valuable metals such as gold, silver, uranium and the platinum group elements, which may only be present at levels of a few grams per ton or less,” according to Tickner.
“We are not aware of any other system capable of doing accurate, on-stream mineralogy, and we have already received considerable interest from industry representatives about our prototype,” Tickner said. “And the ability to detect elements at parts-per-billion levels in an on-stream system is unique.”
Afrox Expands Goldox Technology to Optimize Gold-Leach Effectiveness
Afrox, which claims to be the largest industrial gas and welding supplier in sub-Saharan Africa, showcased its latest Goldox enhancement—a new leach feed diagnostics system developed for in-the-field evaluation of oxygen demand characteristics—at the WorldGold Conference held in Johannesburg, South Africa.
Goldox is a process Afrox offers for the use of oxygen in cyanide-based gold leaching. According to the company, the technology was first introduced to South African gold mines in the mid-1980s and is now used by mines in North America, Australia and South America. Claimed benefits include capital savings on new plant, optimized cyanide usage and potentially lower and stable residue grades. The system can be retrofitted to existing plants.
The Goldox process performs a dual function. Through the introduction of pure oxygen in the preconditioning stage to the ore slurry, the dissolved oxygen concentration is increased, reducing the ore reactivity, resulting in an increased gold leaching rate which improves gold recovery and profitability.
The latest addition to the technology will be made available as a service to Goldox users, comprising a sophisticated mobile unit that can be brought on-site to analyze various dynamics found in the gold leaching processes, yielding immediate diagnostics of the variables that may be influencing the process.
The Goldox suite of technologies now includes leach plant diagnostics, dissolution devices such as the Tri Lance, Hyprox dispersion, as well as the EDR dissolution system. The Goldox system can also be automated to achieve a stable DO setpoint and profile in the leach. The technology, according to Afrox, is quite versatile and suitable for small and large gold operations, as well as for uranium extraction where high pressures may be required.
Part of the Goldox offering is a complete analysis by Afrox specialists of customer processes to determine the suitability of the technology and to establish the best approach to maximize its performance. Afrox, a member of the Linde Group, also offers logistics support for the Goldox system to assure security of supply.
The company also provides a wide range of industrial gases, including the pure gas mixtures required by metallurgical laboratories for use in inductively coupled plasma (ICP) and atomic absorption spectroscopy (AAS) for plant recovery performance testing; special gas mixtures to calibrate gas detection instruments, ensuring plant compliance in avoiding potential exposure to toxic gases and controlling smelter stack emissions; and refrigerants used in refrigeration plants servicing mine shafts and a refrigerant recycling plant for cleaning these refrigerants.
