Various techniques have been used to “clean-up” wet-process phosphoric acid such as precipitation, flotation and adsorption. To address the potential of membrane processes in the phosphoric acid clarification process, this study explores the benefits of membrane techniques as a green separation technique for phosphoric acid clarification in an eco-efficient way through the use of recycling spent reverse osmosis membrane. Regenerated membrane was used to study the phosphoric acid clarification at a laboratory scale. They were immersed in an oxidizer for at most seven days. The samples were characterized systematically before immersion in an oxidant media. In this study, the potential to regenerate spent membranes and application of this media to clarify the 29% P₂O₅ phosphoric acid was demonstrated. This study shows, through experiments, that the reverse osmosis (RO) membranes could achieve a rejection of 70% and 61% for suspended solid and organic matter, respectively. These promising results will pave the way for implementation of these membranes in phosphoric acid treatment. Moreover, besides being economically advantageous, the use of the spent membrane is likely an environmentally friendly route (no waste, no organic solvent and effluent to be regenerated later on).

The utilization of phosphoric acid in various sectors, e.g., food industry, is controlled by the authorized concentration limit of impurities. However, industrial phosphoric acid is contaminated with undesirable impurities (such as F, Al, Fe, Mg, etc.). Herein, this study aimed to evaluate the efficiency of the membrane purification process of pretreated industrial phosphoric acid using a premodified nanofiltration membrane. We demonstrated that the prior pretreatment steps for industrial phosphoric acid allowed the elimination of sulfate, fluorine and arsenic. Further purification of the obtained pretreated phosphoric acid using membrane cells reduced the concentrations of Cd, Al, Fe and rare earth elements by 94.81, 99.30, 99.63 and 96.67%, respectively. The membrane is functionalized by a deposit of a high molecular weight polycationic polymer of polyethyleneimines in order to produce a highly charged membrane surface to enhance the separation efficiency, selectivity and stability of the membrane. We found that the purification process relies on electrostatic repulsion between the functionalized membrane and highly charged ions, and the reduction rate of metals is a cation charge-dependent parameter. The laboratory and industrial pilot scale results showed that this process allows the production of food-grade phosphoric acid.

Phosphate rocks, as well as their derivatives and by-products, are complex minerals that make elemental analysis very complicated. Iodine is commonly found in these matrices, and its concentration must be controlled. The present work describes the development of a novel rapid digestion protocol based on ultrasonic-assisted acid digestion for the determination of iodine in phosphate rock and phosphogybsum samples by Iodometric titration. The developed method occurs at low digestion temperature and uses a dilute nitric acid 5% (v/v) solution instead of concentrated acid. The investigated parameters influencing UAD, were completely optimised using experiments design methodology (DOE). Iodine recoveries from dilute nitric acid digestion without sonication were generally lower overall when compared to UAD results, illustrating the effect of ultrasound on iodine dissolution. This technique effectively addresses iodine volatilisation and sample losses problem encountered while using classical digestions. Method validation included: defining the detection and quantification limit of iodine using this method were about 2.2 and 8 mg.kg⁻¹, respectively, and it's suitable for the proposed application. Moreover, the repeatability and reproducibility, expressed as RSD for phosphogybsum sample was 7%, 8.3% respectively, while for phosphate samples is tacked as the mean of relative standard deviation 3.4%, 3.8%. Additionally, accuracy of the method was assessed by analysing a certified reference material and the iodine concentration was found to be in good agreement with the indicative values for this CRM. Thus, the mean recoveries in fortified sample were between 96% and 107%.The developed method is fast, accurate, and it is applicable to the monitoring of iodine in the phosphate industries.

Herein we report the purification of pre-treated industrial phosphoric acid using pre-modified nanofiltration membranes. We demonstrated that the prior pre-treatment steps of industrial phosphoric acid allow the elimination of sulphate, fluorine and arsenic. Further purification of the obtained pre-treated phosphoric acid using membrane cells reduce the concentrations of Cd, As, Al, Fe and rare earth elements by 94.47%, 82.35%, 99.40%, 99.64% and 96.67%, respectively. We found that this purification process relies on electrostatic repulsion between the membrane and highly charged ions and the reduction rate of metals is a cation charge dependent parameters. The laboratory and pilot scale results show that this process allows the production of food-grade phosphoric acid. Keywords Nanofiltration; Phosphoric acid; Membrane; Functionalization; Purification; Pilot scale