Abstract

The principle of this method is based on the coupling of a conventional complexing ions (metal) by a macroligand and filtration of the complex formed by an ultrafiltration membrane. Unlike ions through the membrane, the complex ligand cation is retained by the latter. The method then allows to recover a purified solution of one part, and a concentrated solution of the other complexes. is particularly suitable for the treatment of effluents containing heavy metal traces (hydrometallurgical plant discharges, discharges from the chlor-alkali industry ...). Compounds conventionally used in operations complexation / ultrafiltration are polyelectrolytes, flexible chain polymers with ionizable groups.

In addition, the complexation is a way to introduce a selectivity in the separation of
cations, depending on the stability of the ligand-complex cation formed. Indeed, the
retention of the metal cations by the ultrafiltration membrane depends on both the retention of the ligand (not always total) and the stability of the complexes formed which depends on the nature of the complexing agent and the pH and the ratio concentrations of ligand / metal.
In this work, we are particularly interested by the complexation of Co (II) and Ni (II)
with the ligand EDTA and recovered by ultrafiltration. The principal aim of this study
is the optimization of the metal complexation conditions with the two ligands , e.i the
pH ,time, the initial concentration of the ligand, the temperature and agitation speed
this is in order to obtain the best outcomes of the metal separation by Ultrafiltration.

The study was been in three stages:
The first consists in the modeling of the two complexation reactions based on the
expressions of the stability constants of all species existing in the field and the
realized mass balances for the two cation and the ligand. After that we obtained a
system of non-linear algebraic equations in which the resolution is done in a numeric
way with the MATLAB 7 software.

For the initial concentration of the cobalt [Co2+] 0= 5.10-4 M =[Ni2+]0, the obtained
results show that the complex Co-EDTA reaches a maximum concentration and the
best stability in the field of pH [6-13], while the complex Ni-EDTA reaches its
maximum in the pH range [6-13].

The second stage is the experimental study which mentions that the concentration of
the residual cobalt, nickel reduces with the increase of the complexing agent
concentration, with the increase of the pH also with the temperature’s increase and
agitation speed. For an initial concentration of cobalt [Co2+] = 5. 10-4 M =[Ni2+], the
optimal conditions for the complexation with cobalt are: (contact time = 30 min
[EDTA]0 = 5.66 10-4 M, pH = 6.5, T= 23 °C and the agitation speed = 500 rounds/
min) , and for the nickel (contact time= 45 min, [EDTA]0 = 5.66 10-4 M, pH=6.6, T=
23°C and the agitation speed = 700 rounds/min) .

The last step is the experimental part of the ultrafiltration of Co-EDTA complex, the
retention of the membrane can reach 80%, mainly for the pressure of 2.5 bar, the complex Co-EDTA can be recovered by the membrane ultrafiltration. The comparison between the calculated and experimental results showed differences.

The comparison between the reactivities of cobalt and nickel with EDTA showed
small differences, this shows that EDTA forms stable complexes with both metal
cations studied.

Keywords: Ultrafiltration, Complexation, Cobalt (II), Nickel (II), EDTA, MATLAB.

Information

Item Type:	Thesis
Divisions:
ePrint ID:	223
Date Deposited:	2014-12-16
Further Information:	Google Scholar
URI:	https://www.univ-soukahras.dz/en/publication/article/223

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