Objective
Now that this initial stage of the research has been concluded, it appears:
- that the process of acidic leaching of the zinc-containing and lead-containing residues with the aid of spent hydrochloric pickling baths can at present be envisaged only for recycling blast furnace sludges, with the exclusion of dust from a steel plant (oxygen converter or electric);
- that, in the case of this steel plant dust, the process may possibly be adopted only as a means of preliminary inertizing when the actual dumping of the residue is not permitted.
The problem of treating steelmaking sludge and dust rich in zinc and lead has not yet been resolved satisfactorily, except where zinc and lead contents are particularly high (eg electric melting shop dust).
A novel and economical solution to this problem is to be developed by carrying out research into the possibilities of treating such sludge and dust with another waste product occurring in integrated steelworks, depleted hydrochloric pickling baths. These are characterized by relatively low free acidity but extremely high potential acidity, if the ferrous iron in the sludge is oxidized and then the ferric salts are precipitated out in the form of goethite, which is an easily filtered insoluble compound.
This procedure should give the baths a high solubilizing capacity, further reinforced by the complexing action of the chloride ions.
The alkaline compounds in the sludge and dusts (ZnO, PbO, CaO, etc) will be dissolved by the acid released by hydrolysis of the ferric salts, whilst the iron oxides and carbon will remain unchanged.
Two successive research phases are planned, as follows:
1) Checking of basic chemical reactions in discontinuous reactors in order to confirm the feasibility of the flow-sheets proposed, define the main operating conditions and establish the order of magnitude of the yield of the different reactions.
Possible interactions between the successive phases will also be studied, in order to detect any incompatibilities and develop suitable solutions.
On completion of this first part of the research an initial technical and financial evaluation will be made of the validity of the process and the conditions of application.
The financial aid granted covers the first research phase only.
2) Selection of a definitive flow-sheet, development of a small-scale continuous treatment unit, and optimization of reactions. This second phase will be proposed to the Commission only after demonstration of the feasibility of the process.
Topic(s)
Call for proposal
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4000 LIEGE
Belgium