Synthesis of crystalline δ-Na 2Si 2O 5 from sodium silicate solution for use as a builder in detergents

Abstract

δ-Na 2Si 2O 5 has been synthesised from a sodium silicate solution and has suitable properties for use as a builder in detergents. The influence of the main variables in the synthesis, i.e. amount of seed, temperature, seed particle size and synthesis time, has been investigated. The presence of the undesirable α and β phases in the product has been detected when seed is not added. The addition of δ phase crystals allows a highly crystalline layered δ disilicate to be obtained. The highest crystallinity, δ phase content and, consequently, the highest Ca 2+ and Mg 2+ binding capacities were obtained when the synthesis was carried out at 725°C for 25 min in conjunction with 20 wt% of seed with a particle size of 0.038– 0.1 mm . Higher temperatures and longer reaction times favour the conversion of δ phase to the more stable α phase, a process that is not desirable because of the low binding capacity of the α phase. Moreover, a comparative study concerning the synthesis from a sodium silicate solution and from amorphous solid silicate is presented.