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I have a machining process that uses a coolant. The coolant, which contains 8-12% triethanolamine, comes in contact with a low melting point alloy during use that contains Cd and Pb. When the coolant is changed out, it tests out as hazardous waste due to Cd and Pb above regulatory thresholds. We treated the coolant with a product that precipitates and removes Cd and Pb from water but it has no significant effect on the concentration of Cd and Pb in the coolant. I am guessing that the TEA, which can act as chelating agent, has formed metal chelates that will not precipitate with our water treatment product. 1) Is there a chemical I can add to the fresh coolant to prevent chelation from occurring? or 2) Can the metal chelates be precipitated or otherwise be removed from the waste coolant prior to disposal?

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    $\begingroup$ How well filtered is the liquid waste? Could there be particles left causing the issue? Also, you might try altering pH, and adding a sacrificial metal, e.g., Zn or Mg, to try to break up the complex (leaving the Cd and Pb on the metal). $\endgroup$ Commented Apr 28 at 21:22

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