Fabrication and evaluation of an attapulgite membrane as the filter for recycling blowdown water from industrial boilers

Abstract

Continuous blowdown water (CBW) from industrial boilers is of great quantity and energy, and therefore worth recycling. According to the data from a long period of monitoring, carbonate and sulfate were documented as the main contaminants in CBW. Herein, an attapulgite (ATP) membrane was prepared on a macroporous Al2O3 support through solid state sintering. The prepared membrane (attapulgite membrane (ATM)) was characterized by mercury porosimetry, scanning electron microscope, X-ray diffraction, and permselectivity analysis in dead-end mode. The optimal sintering temperature was 800 °C based on the morphology of the sintered active layer and its adhesive strength with support. The active layer exhibited a pore size distribution concentrated on 12.7nm with a thickness of about 80μm. In addition, crystal structures of ATP were retained in powder form after sintering. ATM obtained a pure water permeability of 1,411.87Lm–2h–1MPa–1 with the effective retention of carbonate and sulfate through electrical-related interactions. Several ATM filters were also developed and mounted on the boiler blowdown pipe, which had a high rejection rate of alkalinity and dissolved solids in CBW. The volume of wastewater emitted from the low-pressure boiler was reduced, since the filtrate could be recycled as part of the make-up water.