Accurate Process Control Leads to Superior Zinc Production

Precise control of sulfuric acid concentration is vital for efficient leaching of zinc calcine. Binani Zinc, a zinc producer in India, was looking for a reliable method of determining acid concentration that would withstand  harsh conditions and require very little maintenance. The solution was found with in-line conductivity measurement from METTLER TOLEDO.

The process of leaching zinc from zinc calcine (oxidized zinc sulfide) is usually carried out in a two-stage countercurrent process. Firstly, finely ground calcine is leached in a dilute sulfuric acid solution taken from the second leaching stage to produce a first stage leach solution. After suitable purification treatment, zinc is recovered from this solution via a conventional electrowinning process. The residue from the first stage, which still contains a certain amount of zinc, is leached further in a separate tank with electrolyte from the electrowinning operation. Crucial to obtaining high zinc yield from the entire procedure is control of the concentration of the sulfuric acid solution.

Binani Zinc Ltd, India

Since 1967, Binani Zinc Ltd. in Binanipuram, Kerala, India has been using the method described above to produce zinc. Company engineers had employed sample-based lab analysis for acid concentration measurement. However, they found that effective process control was not possible because of the delay between samples being taken, measurements being available, and process adjustments being done. Engineers knew that process yield could be significantly increased if a quicker method of determining acid concentration was used.

Binani Zinc asked METTLER TOLEDO to provide a system for determining acid concentration that offered high repeatability, very low maintenance, a reasonable cost of ownership, and an ability to withstand harsh process conditions.

After discussions it was agreed that indirect acid concentration measurement by determining conductivity in the process medium would be the best solution. Binani Zinc purchased seven identical systems, comprising InPro 7250 PEEK conductivity sensors, M700 transmitters, and InDip 550 PVDF housings.

Process improvement

Before installation of the METTLER TOLEDO systems, acid concentration fluctuated from 30 – 90 gpl. Thanks to the InPro 7250 and M700, that range is now held to a much more satisfactory 55 – 70 gpl, leading to better process control and improved productivity. In addition, plant engineers appreciate the robustness and maintenance-free operation of the InPro 7250. The sensor’s PEEK body resists acids and has no electrodes in contact with the process medium that could become fouled. In combination with the M700 transmitter, engineers find the system easy to use and simple to operate.

Find more about the InPro 7250:

Contact information:

Mettler-Toledo International Inc.

Im Langacher,  Zip Code 8606

Greifensee, Switzerland

E-Mail    :

Phone     : +41-44-944 33 85

Website  :

About Author:

METTLER TOLEDO specializes in the area of precision instruments for professional use. METTLER TOLEDO laboratory instruments are used in research, scientific, drug discovery, and quality control labs, amongst many others in the pharmaceutical, chemical, food and cosmetics industries. METTLER TOLEDO comprehensive industrial solutions cover the various steps in a host of manufacturing processes at many of the same customers that laboratory serves. Solutions range from receiving raw materials through various manufacturing processes, in-line process control and end-of-line packaging control, to logistics and shipping. Increasingly, these solutions are fully integrated into the customer's IT environment, helping automate their workflows. In food retail, our offering for fresh food management ranges from receiving and pre-packaging, to in-store solutions for self-service departments, deli counters, and checkout terminals.

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