Facile extraction and characterization of calcium hydroxide from paper mill waste sludge of Bangladesh

Herein, paper mill waste sludge (PMS) from two different sources has been investigated to extract calcium hydroxide, Ca(OH)2 by a facile and inexpensive extraction process. This green process exploits typical chemical precipitation (CP) in an aqueous medium at room temperature to develop an economically and industrially viable technique for the effective utilization of calcium-containing waste sludge. PMS samples, collected from local paper mill plants of Bangladesh, were the main precursors wherein HCl and NaOH were utilized for chemical treatment. The as-synthesized products were analyzed by a variety of characterization tools including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, Scanning electron microscopy (SEM), and Energy Dispersive X-ray (EDX) elemental analyses. Our studies confirm that the extracted product contains Ca(OH)2 as a major content, albeit it also includes CaCO3 phase formed owing to the inescapable carbonation process from the surrounding environment. The particle size of the synthesized products is in the range of 450 - 500 nm estimated from SEM micrographs. The crystallite domain size of the same estimated from XRD analyses and was found to be ~47 nm and ~31 nm respectively for product-A and product-B considering major (101) Bragg peak of Ca(OH)2. The yield percentage of the isolated products is about 65% for samples collected from both sources.