Formation of Sodium Pentacalcium Sulfate Scale and lts Prevention by the Addition of Additives into the Brinet

The formatien of sodium pentacalcium sulfate scale (Na2SO4, 5CaSO4, 3H2) in the concen, tration process of the ion exchange membrane brine and its prevention by the help of various additives were studied. The formation zone of sodium pentacalcium sulfate was diseussed from the view point ef calcium sulfate transformation in the concentrated brine. Concentration tests were made by the use of a small evaporating apparatus at 75C, concentrating to the concentration-factor 1.3Av5. For the scale prevention were used various additives such as sodium hexameta-phosphate (SHP), sodium carboxyl-methyl cellulose (CMC), citric acid (CA), sodium citrate (SC), poly acrylic acid (PA), sodium poly acrylate (SPA), poly acrylamide (PAA), and Krilium (KM). These additives were introduced to the decarbonated brine, and the brine wa concentrated to the concentrationwfactor 2 with a small evaporating apparatu at 750C. Result are as following 1. The transformation of calcium sulfate in the concentrated brine was determined by the use of solubility of CaSO4, CaSO41/2H2O and CaSO4.2H2O which were measured by the Soga et al. and Egawa at al., and the results are shown in Fig, 2, lt was assumed that the formation zone of sodium pentacalcium sulfate existed between A and C line in Fig.2.2. The result of DTA, TGA and chemical analysis of the adhered scales showed that sodium pentacalcium sulfate was the main constituept of-scale (Fig.6). This phenomenon showed sodium pentacalcium sulfate scale was formed under the condition of No. 2 pan of triple-effect evaporator in the salt-manufacturing factories. 3. The comparison of calcium ulfate concentration in the concentrating brine with the calculated concentration value (Fig. 7), the analysis of constituent of adhered scale, adhesion rate of scale and change in heat-tran fer coefficient (Table 3) revealed that sodium hexametapho phate was the most effective for the inhibition of alcium sulfate deposition and the prevention of odium pentacalciun sulfate formation.