The qualitative determination of the crystal structures in the
residues and mixtures was conducted using a Philips X-Ray
diffractometer (XRD), model PW 3710, using monochromatic Cu Ka
radiation with the following attributes: l ¼ 1.54184 Ǻ,
voltage ¼ 40 kV, current ¼ 20 mA, scan step size of 0.06, count rate
per step of 1 s, and calibrated for 2q using a silicon standard. Sludge
specimens were dried in an incubator at 110 C for 2 h, and the
resulting residues were ground using an agate mortar.