REMOVAL OF DISSOLVED SELENIUM FROM AQUEOUS SOLUTIONS

摘要

Processes for treating aqueous solutions to remove dissolved selenium species, for example in the presence of an excess of sulphate anions, which include the use of strongly basic anion exchange resins, or co-precipitation and adsorption of the selenate (and selenite) with mixed ferrous and ferric iron, or combinations thereof. Co-precipitation and adsorption of selenate may take place in an electrolytic cell in the presence of ferrous and/or ferric iron.

主权项

1. A process for treating an aqueous solution to remove dissolved selenium oxyanions comprising:
(A) an ion exchange process comprising: passing a primary aqueous solution comprising selenate and at least a second anion over a strongly basic anion exchange resin loaded with the second anion, under loading conditions whereby the selenate anions displace the second anion from the resin to produce a selenate loaded resin and an ion exchange discharge solution comprising a lower concentration of selenate than the primary aqueous solution, wherein the second anion is present in the primary aqueous solution in excess of the selenate; treating the selenate loaded resin with a regenerant solution comprising selenate and the second anion under regenerating conditions whereby the second anion in the regenerant solution displaces selenate anions from the selenate loaded resin to produce a selenate laden regenerant solution having a higher concentration of selenate than the primary aqueous solution, wherein the regenerant solution comprises a higher concentration of the second anion than the primary aqueous solution; removing selenate from the selenate laden regenerant solution to produce a selenium depleted regenerant solution, and recycling the selenium depleted regenerant solution to form to the regenerant solution for treating the selenate loaded resin;or
(B) a selenate precipitation process comprising: passing a selenate-containing aqueous solution into a flow-through chamber; contacting the selenate-containing aqueous solution in the flow-through chamber with one or more iron-bearing streams comprising ferrous iron or a ferrous/ferric iron mixture under conditions effective to co-precipitate or adsorb at least a portion of the selenate with the iron thereby producing a selenium-iron precipitate and a selenium depleted discharge solution, the conditions comprising a retention time in the flow-through chamber of between about 5 minutes and about 90 minutes and a pH between about pH7.0 and pH13.0, wherein the one or more iron-bearing streams comprises a total iron content of 100 mg/L or greater; and separating the selenium-iron precipitate from the selenium depleted discharge solution;or
(C) the ion exchange process of (A) and the selenate precipitation process of (B), whereby the step of removing selenate from the selenate laden regenerant solution in the ion exchange process of (A) comprises the selenate precipitation process of (B), the selenate laden regenerant of the ion exchange process of (A) forms the selenate-containing aqueous solution of the selenate precipitation process of (B), and the selenium depleted discharge solution of the selenate precipitation process of (B) forms the regenerant solution of the ion exchange process of (A).