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Category: Refining and Recovery
Subject: Rhodium recovery
I am working on the recovery of Rh from concentrate.
The concentrate contains Fe2O3 92%, TiO2 2%, Nb2O5 0.2%, V2O5 0.3%. Pt is 280 g/ton, Rh is 300 g/ton.
This is roasted at 800ºC with NaHSO4 and then chlorinated with HCl at 80ºC for 2 hours. The ratio of solid to liquid is: 1 kg to 2 litres. The liquid contains 150 g/litre of HCl and the balance is deionised (DI) water.
The filterate obtained is removed. The remainder is boiled at 80ºC, and oxalic acid is added. Then I effect hydrolysis, i.e. it is heated and the reduced liquid volume is made up by addition of DI water. However, no Rh crystallisation occurs.
Do you think it takes time to crystallise or is my mode of working wrong?
Answer
With the quantities you describe, for 1 kg of solid there will only be 300 micrograms of Rh which, in a final volume of 2 litres, is only 150 ppm.
You are using oxalic acid for precipitation, but for precipitation the solubility products of any oxalate salts would need to be exceeded. With these quantities I doubt if this will occur, particularly with the amount or iron you say is present - the iron will consume a large proportion of the Na bisulphate, etc.
Oxalate precipitation is not the usual procedure for precipitating small quantities of Rh. Also, any Fe(III) that has been formed will consume oxalate or any reductant you add.
I suggest you try to analyse the filtrate to see if you have successfully solubilised the rhodium. If you have, then perhaps add a large amount of a strong reductant, such as formic acid.
Answer posted 19 August 2005
Submitted by: Mr Sharad Shah
Affiliation: M/s.Alchemist Processors
Answered by: David Boyd
Affiliation: Technology Manager, Refining Technology, Johnson Matthey Technology Centre