| 主权项 |
1. A method of purifying phosphoric acid comprising:
(a) providing a pre-treated wet phosphoric acid feed containing:
(i) 2-62% phosphoric acid, expressed as a percent weight of P2O5 in said feed;(ii) a sulfate concentration of at least 15 ppm, per each 1 percent weight of said P2O5 in said feed; and(iii) metallic impurities including iron, aluminum, calcium, magnesium, and chromium, a total feed concentration of said iron, aluminum, calcium, magnesium, and chromium being at least 10 ppm, per each 1 percent weight of said P2O5 in said feed; (b) subjecting said pre-treated wet phosphoric acid feed to a first nanofilter in at least a first nanofiltration stage, to obtain a first permeate and a first reject; (c) treating said first permeate to produce sulfate solids in a partially treated phosphoric acid stream; (d) removing at least a portion of said solids from said phosphoric acid stream; and (e) subjecting said phosphoric acid stream to at least a second nanofilter in at least one additional nanofiltration stage, to obtain a purified phosphoric acid in a second permeate, and a second reject, said second permeate containing:
(i) a concentration of 2-62% phosphoric acid, expressed as a percent weight of P2O5 in said second permeate;(ii) a sulfate concentration of less than 10 ppm per each 1 percent weight of said P2O5 in said second permeate; and(iii) metallic impurities including iron, aluminum, calcium, magnesium, and chromium, a total concentration of said iron, aluminum, calcium, magnesium, and chromium in said second permeate being at most 5 ppm, per each 1 percent weight of said P2O5 in said second permeate. |
