Preparation and performance of multi-ionic composite coagulants based on coal gasification coarse slag by one-step acid leaching

Coal gasification coarse slag (CGCS) is a kind of solid waste generated from coal chemical industry. A series of CGCS based multi-ionic composite coagulants were achieved with one-step acid leaching process, optimizing by HCl concentration and acid leaching time. The results indicated that the optimal Coagulant-3.0 showed a remarkable performances on kaolin simulated wastewater with removal efficiency of 98.0% turbidity, 98.0% NH4-N, and 37.0% CODCr, which were of 91.8%, 77.4% and 69.9% for domestic sewage, respectively. Coagulant -3.0 was further characterized by X-ray Fluorescence Spectrometry (XRF), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM). It was found that Coagulant -3.0 was mainly occupied with Fe, Ca, and Al. The good fitting of the pseudo-second-order kinetic model revealed that the co-existence of multi-ions played a synergistic role in the improvement of coagulation performance. Furthermore, the coagulation mechanisms of charge neutralization, adsorption bridging, and sedimentation netting were basically investigated. The work was unique in developing a novel, cost-effective strategy for the production of coagulants based on the intrinsic constituents of CGCS, and providing a safe and efficient way to dispose of CGCS. Additionally, it is potential to offer an alternative pathway for increasing the additional value of the coal chemical industry.