Comparative study on the use of zeolite and precipitation agents to retard scale formation in the seawater pretreatment process

Abstract

The scale formation in heat transfer surfaces in seawater desalination plants by multi stage flash processes (MSF). This scale is formed during the precipitation of salts containing in seawater such as calcium and magnesium carbonates. The pretreatment is based on the removal of the calcium and magnesium cations from seawater, using zeolite as cation exchanger and precipitator agents as: lime, soda ash, and mixture of soda ash with soda. DRX, SEM, and EDX analyses were employed to characterize the zeolite before and after pretreatment so as to demonstrate the change composition on the zeolite surface. The results revealed that the pretreatment by a mixture of soda ash (13g/L) and soda (4g/L) favor the precipitation of calcium and magnesium ions. The calcium and magnesium ion concentrations in seawater were reduced, respectively, from 620 mg/L and 644 mg/L to 5 mg/L and 9.11 mg/L.