Abstract
Streams of waste mixed acids from conventional wet etching processes contain high levels of H3PO4, which warrant recycling. This investigation is the first to use metal organic framework UiO-66 and UiO-66-NH2 to adsorb phosphoric acid from waste mixed acids from the world's largest semiconductor foundry, a synthetic HNO3H3PO4HAc mixture, and 85% phosphoric acid. Both UiO-66 and UiO-66-NH2 have high capacities to adsorb H3PO4 in extremely acidic solutions. The Langmuir adsorption capacities (qmax’s) of UiO-66 for waste mixed acids and a synthetic HNO3H3PO4HAc mixture on UiO-66 at 25 °C are 3360 and 8,510 mg-H3PO4/g, respectively, and that of 85% phosphoric acid on UiO-66 is 4,790 mg-H3PO4/g. The qmax of UiO-66-NH2 for phosphoric acid from 25% to 75% waste mixed acids is 4550 mg-H3PO4/g, which exceeds that of UiO-66. The corresponding P:Zr ratio for adsorbed MOF is in the range 6.2‒13.5, suggesting that the tested MOF crystals are super-adsorbents of phosphoric acid under extremely acidic conditions.
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