Optimisation of a purification method for metal-containing wastewater by use of a Taguchi experimental design

A procedure for purifying waters polluted with metal ions has been designed. The method is based on the precipitation of metals as magnetic ferrite from the alkalinised solution containing iron(II). The working conditions were optimised by using a Taguchi L9(34) experimental design in order to minimise the total residual concentration (TRC) of metal ions in solution. A statistical analysis of the experimental data revealed the most influential factor to be the Fe(II)/metal concentration ratio (F), with a 29.5% contribution, followed by pH (P, 5.2%) and time (H, 2.3%). On the other hand, temperature (T) had little effect on the purification efficiency (1.0%), whereas noise (N, KMnO4) was found to contribute by as much as 22.1%. Maximal purification efficiency (99.99%) is achieved when wastewater samples are treated for 3 h at 50°C and pH 10 in the presence of iron(II) in a ratio Fe(II)/total metal of 15. In these conditions, the process efficiency is also the least influenced by variability in the sample composition, which validates the proposed procedure.