An environment-friendly method of utilizing spent pickle liquor is sought.
The pickling process uses HCl to pre-treat the metal surface and removes unwanted surface impurities like rust etc. This generates a considerable quantity of Spent Pickle Liquor (SPL) which primarily consists of Ferrous Chloride. To make the best use of this waste, we intend to convert this SPL into iron oxide. One of the known methods of treatment of this type of SPL is neutralization with an Ammonia solution followed by treatment with lime to recover Ammonia. However, this method produces excessive sludge (in this case Calcium Chloride) which creates further challenges and also has slow precipitation kinetics.
The other method is pyro-hydrolysis. However, this process is very energy-intensive and it requires natural gas which makes the whole process very expensive. Moreover, it also produces a considerable amount of stack emissions containing HCl, particulate matter & chlorine which are very harmful to the environment and cannot be discharged easily.
Solutions are sought for either of the following: