Recent progress in heavy metals extraction from phosphoric acid: A short review

Abstract

According to the global mineral acids market, phosphoric acid is the second largest produced acid, after sulfuric one. It is mostly manufactured under thermal or wet process and due to its low cost, this latter remains the most widely adopted. However, one major drawback of this process is the presence of a wide variety of suspended, dissolved organic impurities and heavy metals. Many of these elements are disadvantageous to acid quality that end up later in many industrial products like detergents, food, pharmaceutical industries, and fertilizers. Among these impurities, Cd, Cr, Ni, As, Fe, Al, Cu, etc, endanger animals, fauna/flora, and humans as they tend to accumulate in biological systems. Consequently, the wet phosphoric acid (WPA) needs to be purified before any use. Recently, several industrial processes for heavy metals removal from WPA, including solvent extraction, ion exchange, adsorption, flotation, precipitation, and membrane processes have been intensively reviewed. However, the high cost of these current processes prevents wide-scale applications and still require further investigation. Herein, the current short review compares and evaluates the various industrial processes for removing heavy metals from WPA, beginning with ion exchange, which has recently become a more popular technique in this area. It also discusses solvent extraction, precipitation, adsorption, flotation, and even membrane processes that may prove to be a useful alternative. Moreover, comparisons are made between the efficiency of various techniques for heavy metals removal, and both their advantages and drawbacks are highlighted. This review also updates some recently published empirical/academic research with an emphasis on industrial applications related to this field.