Method for purification of acids from materials comprising acid and salt

A method of separating acid from an aqueous feed stream comprising acid and salt, comprising cations and anions, in an apparatus comprising at least two bipolar membranes, a first bipolar membrane and a second bipolar membrane, each bipolar membrane comprising a cation layer and an anion layer, at least one anion membrane and at least one cation membrane, the anion membrane and cation membrane being between the two bipolar membranes, the anion membrane being between the cation layer of the first bipolar membrane and the cation membrane, and the cation membrane being between the anion layer of the second bipolar membrane and the anion membrane, there being an intermediate compartment between the anion layer and the cation membrane, a feed compartment between the anion membrane and cation membrane, and a product compartment between the cation layer and the anion membrane, comprising the steps of:

• feeding an aqueous feed stream comprising strong acid and metal cations to the at least one feed compartment;
• feeding an aqueous product stream to the at least one product compartment;
• feeding an acidic or neutral intermediate aqueous stream to the at least one intermediate compartment;
• applying a sufficient electrical potential across the apparatus to cause a direct current resulting in the introduction of H.sup.+ from the bipolar membrane into the product compartments and transport of anions from the feed across the anion membrane into the product compartment;
• removing the resulting product stream from the product compartment;
• removing the resulting intermediate stream form the intermediate compartment;
• and
• moving the resulting feed stream from the feed compartment.

A method comprising the steps of:

• feeding a solution comprising salt and an acid to a feed compartment of a two compartment acid purification unit comprising at least one bipolar membrane comprising a cation layer and an anion layer, wherein each bipolar membrane is between at least one first anion membrane and at least one second anion membrane, there being a feed compartment between the anion layer and the at least one first anion membrane;
• splitting the solution of salt and acid to form a first salt stream and a first acid stream;
• feeding the first salt stream to a feed compartment of a three compartment water splitter comprising at least two bipolar membranes, a first bipolar membrane and a second bipolar membrane, each bipolar membrane comprising a cation layer and an anion layer, between the two bipolar membranes at least one anion membrane and at least one cation membrane, the anion membrane being between the cation layer of the first bipolar membrane and the cation membrane, and the cation membrane being between the anion layer of the second bipolar membrane and the anion membrane, there being an acid compartment between the anion layer and the cation membrane, a feed compartment between the anion membrane and cation membrane, and a product compartment between the cation layer and the anion membrane;
• and
• splitting the first salt stream to form a second acid stream, and a second base stream comprising a base and optionally salt, and a dilute salt stream.