Acid regeneration

A process for the regeneration of hydrochloric acid from spent acid leach liquor containing iron chloride in aqueous solution comprising the steps of:

• a) concentrating the spent acid leach liquor by introducing the spent acid leach liquor into a preconcentrator by a venturi or spray system and contacting with superheated gas from the fluid bed roaster of step (e) to form a liquid concentrate;
• b) transferring the concentrated solution to a pelletiser of the blunger or a rotating disc or drum wherein pellets are formed from a pellet mixture which is formed and controlled to between 12% and 14% free water by weight by recycling, to the pelletiser, dried solids from the roaster of step (e), from the screening of step (d), or from dust removal cyclone of step (e), with waste liquid from the preconcentrator of step (a), as required;
• c) feeding the pellets from the pelletiser to a rotary drier where the pellets are dried with a concurrent hot gas stream with operating conditions within the drier being within the ranges:
• ______________________________________ inlet gas temperature 600.degree. C.-800.degree. C. inlet moist solid feed 50.degree. C.-80.degree. C. outlet gas temperature 160.degree. C.-180.degree. C. outlet dried pellets 130.degree. C.-150.degree. C. ______________________________________
• d) screening the pellets with oversize being sent to a mill, undersize being recycled to the pelletiser, and the remainder, screened pellets being delivered to the roaster of step (e);
• e) roasting the pellets in a roaster and feeding the superheated gas stream containing HCl, excess O.sub.2, diluent N.sub.2, and water vapor from the roaster to the preconcentrator after removing dust from the gas stream by a cyclone with a portion or all of the dust being returned to pelletiser and the heat from the gas stream being used to concentrate the spent acid;
• and,
• f) delivering the HCl gas offtake from the preconcentrator via a demisting cyclone to an adiabatic absorber where weak acid liquor and water are added to absorb the HCl in the gas offtake, and cooling the output of the absorber to form a HCl azeotrope.

An apparatus for the regeneration of hydrochloric acid from spent acid leach liquor containing iron chloride in aqueous solution, comprising:

• a) a preconcentrator to concentrate a spent acid leach liquor;
• means for feeding the spent acid leach liquor into the preconcentrator, wherein said means for feeding the spent acid leach liquor comprises a venturi or spray system;
• means to recycle a waste liquid from the preconcentrator to the pelletiser of step (b);
• b) a blunger or a rotating disc or drum pelletiser;
• means to feed the concentrated spent acid leach liquor from the preconcentrator to said pelletiser;
• wherein in the pelletiser, pellets are formed from a pellet mixture which has between 12% and 14% free water by weight by recycling dried solids from the roaster of step (e) or from the screening device of step (d) or from the dust removal cyclone of step (e) with waste liquid from the preconcentrator of step (a), as required;
• c) a rotary drier, means to feed the pellets from the pelletiser to the rotary drier wherein the pellets are dried with a concurrent hot gas stream with operating conditions within the drier being with the ranges:
• ______________________________________ inlet gas temperature 600.degree. C.-800.degree. C. inlet moist solid feed 50.degree. C.-80.degree. C. outlet gas temperature 160.degree. C.-180.degree. C. outlet dried pellets 130.degree. C.-150.degree. C. ______________________________________
• d) a screening device for the dried pellets, means to deliver the dried pellets from the rotary drier to the screening device, means to send the oversize to a mill, means to recycle the undersize to the pelletiser, and means to deliver the remainder, screened pellets to the roaster of step (e), where hydrolysis occurs;
• e) a roaster for hydrolyzing the pellets, means to deliver the superheated gas stream containing HCl, excess O.sub.2, diluent N.sub.2, and water vapor from the roaster to the preconcentrator, the heat from the gas stream used to concentrate the spent acid leach liquor, wherein said means to deliver the superheated gas stream includes a cyclone between the roaster and the preconcentrator to remove dust from said gas stream and means to recycle at least a portion of the dust to the pelletiser;
• and,
• f) a HCl absorber, means to deliver the HCl gas offtake from the preconcentrator to the HCl absorber wherein said means to deliver the HCl gas offtake contains a demisting cyclone between the preconcentrator and the HCl absorber.