Chemistry of inorganic compounds – Halogen or compound thereof – Hydrogen halide
Patent
1994-08-24
1997-06-03
Nguyen, Ngoc-Yen
Chemistry of inorganic compounds
Halogen or compound thereof
Hydrogen halide
423488, 423DIG1, 23313R, 422185, 422189, 422209, C01B 703, C23G 136
Patent
active
056351526
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates particularly to regeneration of hydrochloric acid from the iron chloride liquor that results from the leaching of iron from ilmenite, to form synthetic rutile. It applies also to regeneration of hydrochloric acid from pickle liquor produced from treating the surface of steel with hydrochloric acid.
The relevant reactions for ilmenite are:
BACKGROUND ART
Because of the cost of new acid, and/or the cost of disposal of iron chloride liquor, the commercial use of hydrochloric acid as a leachant for ilmenite depends on the availability of a technically viable and cost-effective method of regenerating and recovering the hydrochloric acid.
Regeneration of hydrochloric acid is in common use in the steel industry world-wide. For example the acid is used for cleaning steel and wire before galvanising. This process is known as "pickling" and the resultant liquors, consisting largely of iron chlorides and some free acid, is known as "pickle liquor".
The regeneration technology uses either a spray roasting, (Ruthnet), process, or a fluidised bed, (Lurgi), process, both of which produce by-product iron. The reactions:
In both cases the acid can be regenerated by hydrolysis of the iron chlorides. Excess water is removed by heat, and the iron oxide as dust, or as a pellet by-product.
Although the hydrolysis reaction is exothermic (.DELTA.H800.degree. C.=-112.6kJ [-26.9kcal]) the quantity of water that has to be boiled off requires an external heat source.
The principal difference between regeneration of pickle liquor and ilmenite leach liquor is that a significantly greater volume of liquor has to be processed when ilmenite is leached in commercial quantities, than is commonly necessary in the steel industry.
Simplistically, this requires either a very much larger reactor or multiple reactors for an ilmenite leach operation, the size or number required depending on the volume constraints imposed by reactor design.
The volume of concentrated iron chloride liquor which can be injected into a Lurgi--type fluidised bed reactor is limited by the need to achieve uniform distribution of liquor over the whole fluid bed. A large increase in feed volume cannot be accommodated by simply increasing reactor size (diameter).
As an example, the leach liquor from a 50,000 tonnes per year synthetic rutile production facility is estimated at approximately 54 tonnes per hour. Using the Lurgi pickle liquor regeneration technology, 4 reactors would required. The system described herein would require only a single reactor.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a process for the treatment of spent acid leach liquor containing iron chloride in aqueous solution including the steps of concentrating the aqueous solution to form a liquid concentrate, and forming the liquid concentrate into pellets. Additionally, the pellets may be dried and sized. The pellets are formed by adding dried solids or liquid, as the case may be.
According to a second aspect of the invention there is provided a process for the regeneration of hydrochloric acid from spent acid leach liquor containing iron chloride in aqueous solution including the steps of in sequence, concentrating the aqueous solution to form a liquid concentrate, pelletising the liquid concentrate to form pellets, and hydrolysis of the pellets in a reactor.
Additionally, the pellets may be dried and sized before hydrolysis in a reactor.
The reactor is preferably a fluidised bed reactor but may also be a rotary kiln or other known type of reactor. The hydrochloric acid given off by the hydrolysis reaction is then recovered in a hydrochloric acid absorption circuit well known in the art.
Preferably, the iron chloride in aqueous solution, the leach liquor, is concentrated to a nominal 250 g/L (grams per liter) of iron (equivalent to 500 g/L of 40%FeCl.sub.2).
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention will now be described with respect to FIG. 1, which shows a flow sheet o
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Austpac Gold N.L.
Nguyen Ngoc-Yen
Schindler Edwin D.
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