URANIUM EXTRACTION FROM SEAWATER USING CHROMIC ACID PRE-TREATED POLY(ACRYLONITRILE) AMIDOXIME FIBERS

Abstract

Uranium extraction from seawater using chromic-acid-treated amidoxime adsorbent was studied. Chromic-acid-treated amidoxime fibers were synthesized based on the simultaneous irradiation grafting method at low temperature. Low-density polyethylene (LDPE) fibers were treated with chromic acid for up to 90 minutes. After the treatment, fibers were submerged in 60 : 40 acrylonitrile : methacrylic acid monomer by volume and irradiated with gamma ray from Co-60 for a total dose of 40 kGy. The maximum grafting efficiency of about 90% occurred at 20 minutes of chromic acid treatment time, which was as much as 30% higher than literature-reported values. Cografted fibers were converted into amidoxime fibers by reaction with hydroxylamine hydrochloride solution for 75 minutes, obtaining the amidoxime group density of 2.65 mol/kg. Chromic acid pre-treated amidoxime fibers submerged in Andaman seawater with the average temperature of 30oC for 4 weeks exhibited the uranium adsorption capacity of 2.06 g-U/kg-adsorbent, which was 37% higher than literature-reported values. These significantly-increased grafting and adsorption efficiencies were attributed to the increased surface area of LDPE fibers appropriately treated with chromic acid. Study on the usage repeatability of chromic-acid-treated amidoxime fibers revealed that the adsorption capacity reduced to about 65% after 8 cycles of repeated usage. Uranium concentration in Thailand's seawater was analyzed to be around 3 ppb, regardless of location and depth of seawater.