Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter 55.4.14 Upgrading of phosphogypsumDescriptionIt appears that many of the impurities present in phosphogypsum are enriched in the smallestgypsum particles. Among these impurities are mercury, the common heavy metals, theradionuclides and the lanthanides. By separating the particle size fraction with the smallestparticles, the quality of the remaining gypsum can, therefore, be improved substantially.Separation can be achieved by passing the gypsum through a hydrocyclone, as has beendemonstrated on a pilot scale by Kemira and Hydro Agri in the Netherlands [29, RIZA, 2000].In this case, only 4 % of the total amount of gypsum was separated as fines. Application of thistechnique on a commercial scale would not require larger hydrocyclones than those used in thepilot scale, but would require multiple hydrocyclones and therefore scale-up should not be aproblem.An additional advantage of the separation of the smallest particles from the gypsum slurry canbe an improvement in the washing and filtering characteristics of the gypsum. Pilot plant tests atKemira and Hydro Agri in the Netherlands showed that upon washing and filtration of theremaining slurry after particle size separation by means of a hydrocyclone, a substantial amountof P 2 O 5 was still removed from the gypsum despite the fact that Kemira employs a repulp filterin its regular process. Hence, it should be technically possible to return these P 2 O 5 values to theprocess, thus increasing the overall P 2 O 5 efficiency. After vacuum filtration, a gypsum cakeremains with a moisture content of less than 10 %. Such a value is required by the gypsumindustry for the further processing of the gypsum to products.The fines that are separated in the hydrocyclone are released as a dilute slurry (0.5 – 1 wt-%). Itis difficult to find a useful application for this fraction because of the relatively high impuritycontent of the fines. What remains then are the two basic options for disposal discussed above,namely discharge to sea or storage on land. In the latter case, the fines will first have to berecovered from the slurry, e.g. by filtration.Achieved environmental benefits• cleaner phosphogypsum for re-use or disposal• potential for increasing the P 2 O 5 efficiency of the production process.Cross-media effects• electricity consumption• the resulting high impurity fraction needs consideration.Operational dataNo information provided.ApplicabilityGenerally applicable, but not demonstrated on a commercial scale.EconomicsCost benefits if the phosphogypsum can be valorised.Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 249