The treatment of phosphogypsum with zeolite to use it in binding material

In Lithuania, there are accumulated large amounts of fertilizer by-product - phosphogypsum and there is a lack of sources of natural gypsum. Recycling of by-product is one of the effective solutions of its disposal problem. The paper describes an investigation of the hydration behavior of a phosphogypsum with zeolite (hydrosodalite) addition using ultrasound treatment. Two ultrasound treatment durations: 0.5 min and 2 min were used. It was found that hydrosodalite is an effective adsorption additive for acidic contaminants (solvable P2O5 and F) present in phosphogypsum, which allows regulating the phosphogypsum hydration and setting time. The compressive strength of samples containing 5% hydrosodalite and with 2 min sonication is 35% higher, than the compressive strength of samples without additive and sonication. In this case, the positive effect of sonication and of hydrosodalite additive is combined. Phosphogypsum as a residue from the phosphate fertilizer industry is classified as a Naturally Occurring Radioactive Material (NORM). Therefore, when it is used as an additive component to building materials radioactivity content must be checked. The different amount of the various radionuclides within the natural radioactive decay series, such as that of 226Ra, 228Ra, 228Th, 40K, and 210Pb were measured by high resolution gamma spectrometry. The results showed that activity concentration of natural radionuclides as 226Ra, 228Ra, 228Th, 40K are below the clearance limit and activity concentration indices calculated for all materials used for experiments met the existing criteria allowing to use them for construction purposes.