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Kinetics and equilibrium studies of cadmium removal from cadmium phosphate by exchange reaction with cation ions

Yassine Zalim, Abbès Benayada, and Zakia El Ahmadi

Department of Process Engineering, Mohammadia School of Engineering, Mohammed V University in Rabat, Rabat, Morocco



Received: 27 October 2020  Accepted: 7 January 2021


In recent years the presence of cadmium in phosphates ores used in the fertilizers industry has generated a lot of discussion which has prompted governments and authorities to put in place regulations that limit the use of phosphates and derivatives with cadmium contents exceeding certain limits. This work focuses on the study of the exchange reaction between cations ions and cadmium as a technique for reducing the cadmium content in phosphates by hydrometallurgical processes. The study was carried out using a synthesized precipitate of cadmium phosphate. The solubility study of the cadmium phosphate in water shows that it’s a very stable precipitate while it’s was very soluble at acidic pH. The solubility results and values agreed with those theoretically predicted. The exchange between cadmium and zinc is a thermodynamically possible equilibrium reaction that have been confirmed by a X-ray fluorescence analysis. The experimental results showed that the studied reaction reaches equilibrium in 10 h and that interesting cadmium exchange efficiencies can be achieved, for an initial mass ratio Zn/Cd of 2, the cadmium exchange efficiency was 39% and 72%, respectively, after 4 h and 10 h. The exchange reaction between zinc ions and cadmium phosphate was found to be a kinetic equilibrium and slow process, best described by the product layer diffusion control model with a reaction rate constant (k=0.0001 {mathrm{mn}}^{-1}). The calcium ions presence at high concentrations (> 0.5 M) in reaction medium was found to have a slight effect on cadmium exchange efficiency.

Keywords: Cadmium; Phosphate; Cation exchange reaction; Kinetics

Full paper is available at

DOI: 10.1007/s11696-021-01505-1


Chemical Papers 75 (6) 2655–2665 (2021)

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