Electricity + Control January 2018

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PRESSURE + LEVEL MEASUREMENT + INSTRUMENTATION

Extracting more for less in Solvent Extraction Process

Copper is one of the few metals that occur in nature in a directly usable metallic form, also known as native metals, as opposed to needing extraction from an ore. This led to very early human use, from 8 000 BC. It was the first metal to be smelted from its ore 5 000 BC, the first metal to be cast into a shape in a mould 4 000 BC and the first metal to be purposefully alloyed with another met- al, tin, to create bronze 3 500 BC. In the middle ages, the oxidised layer of copper was naturally leached by water, depleting the upper layers of oxidised ore and re- vealing the rich copper laden solutions.This prompted miners to dig deeper, heap the ore and leach it out. This is known as hydrometal- lurgical production, the extracted solvents can be electro-won, and almost pure copper anodes produced. The pyrometallurgical method uses commination (pulverisa- tion), flotation, smelting and converting to produce anodes. The cemented copper that is produced by precipitation in the leaching process can be added to the smelting process for further process- ing to anodes. During this cementation (iron precipitation) copper is produced by running the pregnant leach solution through a pile of scrap iron or steel. An electromechanical process takes place, and the copper precipitates onto the iron/steel, which in turn dissolves into the solution. It detaches as flakes or powder. The pregnant leachate that is produced from the leaching pro- cess, will contain the leaching agent, either water or H2SO4 for oxide ores. Acid cure and acid-ferric cure are used for mixed ores. Some plants use an acid/kerosene mix. The process has to remove and recover the copper from the leachate, and remove impurities. This process has to be controlled, and as we know, when we measure, we can control. Ores that have been mined, crushed and dumped on impervious pads, are usually sprinkled or sprayed with the leaching solution, in the heap leaching process. Ponding, flooding or trickle systems can be used for dump leaching. The pregnant liquor is then fed to a solvent extraction plant, which can be optimised by various methods. Endress+Hauser sug- gests that by measuring the pH, Conductivity and Interface Levels, the process can be managed and optimised for maximum extrac- tion, and minimum wastage. Pressure instrument calibration is a significant part of the main- tenance workload in process plants that requires a high level of accuracy and repeatability. Comtest is offering the latest Fluke 729 Automatic Pressure Calibrator - simplifying the calibration process by automating pumping to the precise test pressure, improving calibration integrity by compensating for minor leaks, and automat- ically documenting the pressure calibration process to meet com- pliance and regulatory requirements. With the rugged, portable 729, technicians simply input a tar- get pressure and the calibrator automatically pumps to the desired set-point while the internal fine adjustment control stabilizes the pressure at the requested value, delivering more accurate results

Solvent Extraction Liquid Flow Most important in the solvent extraction phase (sx) is detection and monitoring of the depth of the organic phase.The copper is trapped in the top layer. Automation is the norm in modern plants, since this does away with manual dipping, and the subsequent errors that it can produce. To this end, with the aid of Sensorfusion, En- dress+Hauser has taken the reliability and accuracy of our guided wave radar and capacitance level, and combined it into one device. It will simultaneously provide a reliable and accurate measure- ment of the top level and interface levels, even in emulsion layers. To accurately assure the correct metal extraction, we need to measure the conductivity of the settling chamber. This measure- ment will ensure that we have control of the transition stage from organic to aqueous. If not correctly controlled, this may cause “mud”, and as a result - plant downtime and wastage of additives. We use the Indumax CLS50D sensor, and a CM44x for this measurement. The CLS50D is an inductive conductivity sensor that can with- stand high temperatures and has high chemical resistance. It has the added advantage of having Memosense digital technology. To accurately control our addition of solution, and the returned aqueous raffinate, we need to know the pH values. For this we use the CPF81D PH sensor. It is a robust, low maintenance sensor with Memosense digital technology. We scratched on the surface of the extraction processes. Uranium, gold, palladium and platinum are commodities that can go through the same process, but with differences in the refining process. Enquiries: Pieter Andjelkovic. Email piet.andjelkovic@za.en- dress.com or susan.buitendag@za.endress.com and speeding the calibration process. Fluke 729 features: • Automatic pressure generation and control for multiple tests to 300 psi, (20 bar, 2 MPa) • Easy calibration documentation using defined templates for transmitters and switches. • HART communication enabling mA output trim, trim to applied values, and pressure zero trimming of HART pressure transmitters • Measurement of mA signals on transmitter outputs and sourc- ing and simulation of mA signals for testing I/Ps and other mA loop devices Enquiries:Tel. +27 (0) 10 595 1821 or email sales@comtest.co.za

Fast and accurate automatic pressure testing and documentation

36 Electricity + Control

JANUARY 2018