Desalination of Saline Sludges Using Ion-Exchange Column with Zeolite

Abstract

A flushing process followed by a zeolite based ion-exchange process were developed for the treatment of saline sludges from oil and gas exploration sites. The particle size distribution of sludge sample indicated the presence of very fine sand and clay. The electrical conductivity of the sludge was 42.2 dS m^-1 indicating very saline sludge and the Cation Exchange Capacity (CEC) was 40 cmoL kg^-1 which was very suitable for ion-exchange process. A 500 g sample of saline sludge (containing CaCl₂:MgCl₂:NaCl ratio as 1:1.16:36.61) was washed using demineralized water in a mixed reactor and the sludge was allowed to settle for 36 h. The optimal number of washes was determined to be two washes with an overall salt removal efficiency of 94.47%. The treated sludge contained 515 mg salt kg^-1 sludge (or 0.05% w w^-1) and was suitable for agricultural application. The washwater was passed through a Mountain Stronach zeolite (chabazite) based ion-exchange column for salt reduction. The sodium salt removal efficiency was 75.34%. This was increased to 99.79% when using two ion-exchange columns. The Ca and Mg ions were under regulatory limits and required no further treatment. The final salt concentration in the wash water was 314.0 mg L^-1 which was below the limits established by the Canadian Guidelines. For complete removal of total salts, a series of ion-exchange columns with different zeolites (for removal of NaCl, MgCl₂ and CaCl₂) will be required.