Reactive silica additives, such as clays, can increase the filterability of phosphogypsum (PG) during wet phosphoric acid production from phosphate rock (PR). In this study, the effect of adding inexpensive fly ash waste (34 kg per t PR) together with lower quantities of pure silica (8.5 kg per t PR) on the radioactivity of PG was investigated. The addition of fly ash waste/pure silica reduced the radiological activity of the PG by roughly 30%. The reduction was attributed to decreased activities from 238U (60% reduction) and 226Ra (30% reduction) in PG. Besides, P2O5 losses were slightly decreased.

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High content magnesium in phosphate and phosphoric acid affect negatively the performance and operating condition in phosphate industry. While for a content more than 0, 3% in phosphate increase the P2O5 losses during phosphate digestion and filtration, also increase steam consumption and solid settling kinetics during concentration. In this work, the removal of magnesium from phosphoric acid by precipitation in one of the compounds MgAlF5 or MgAl2F8 was studied. Magnesium precipitation is achieved by the simultaneous addition of aluminum and fluorine. The experimental design methodology was used to carry out this work. Tests were conducted according to the NEMRODW software using industrial quality phosphoric acid. The screening study of parameters affecting the removal efficiency of magnesium from industrial wet phosphoric acid showed that from the following parameters: temperature, F/Mg and Al/Mg ratios, aluminum form and fluorine form, only temperature and F/Mg ratio have an effective influence on magnesium removal. The optimization of magnesium removal from phosphoric acid was performed according to the response surface methodology using a composite matrix. By applying this methodology, the optimum parameters corresponding to a maximum magnesium removal efficiency in phosphoric acid were determined. The values of the optimum parameters obtained by this method are T?=80?C, ratio Al/Mg=1 and F/Mg= 16.

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Phosphoric acid sludge is one of the prominent problems in the phosphate industry. Its production is cooccurred by large losses of P2O5 that affect the process performance. Management and valorization of this waste is a key issue. For the industrial application in solid-liquid separation, selecting the suitable technique for an efficient separation is a fundamental factor. Most of the separation processes fail because of insufficient development effort in the laboratory phase and misunderstanding of separation objectives. The aim of this work is to deal with the P2O5 losses by studying their recovery from phosphoric sludge using a physical solid-liquid separation technique. Hence, laboratory tests have been conducted using vacuum filtration, centrifugation, and press filtration. The comparison was based on three requirements: the liquid recovery rate for each method, the amount of P2O5 recovered, and the solid content remaining in the recovered acid. Results showed that press filtration gave the higher performance of P2O5 recovery, up to 88, 90%, followed by the vacuum filtration with 69.81%.and then the centrifugation with 80.91%.