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Low-rank coals are generally processed with wet methods including washing, flotation, etc. Fine-sized tailings of these processes are discharged to tailing ponds with a significant amount of associated water which contains a high amount of dissolved ions. These tailings should be dewatered employing coagulation/flocculation in terms of technological and environmental aspects. In this study, the coagulation/flocculation behavior of coal processing plant tailings obtained from Manisa, Turkey was investigated in the presence of monovalent (Na + , K +) and divalent (Mg 2+ , Ca 2+) ions and an anionic flocculant (SPP-600). First, the coagulation properties of coal tailings were determined. Then, the flocculation experiments were carried out, and the turbidity values of the suspensions were measured. Moreover, the sizes of the flocs were determined using a laser diffraction particle size analyzer to analyze the strength of the flocs. The results of the coagulation experiments showed that while divalent ions were more effective at 10-1 mol/dm 3 , higher settling rate and lower turbidity values were obtained in the presence of monovalent ions at 1 mol/dm 3 concentration. The optimum flocculant dosage was obtained as 150 g/Mg from the flocculation experiments. The floc size and strength measurements indicated that the larger flocs were obtained with Na + than Ca 2+ in the presence of the flocculant. The strongest flocs were obtained at 10-1 mol/dm 3 Ca 2+ + 150 g/Mg flocculant. It can be concluded from this study that the coagulation followed by the flocculation method can be employed to obtain fast flocculation behavior and low turbidity for the dewatering of coal tailings.

L ignite coal, which has a large share in world coal reserves, must be subjected to coal preparation processes in coal washing plants due to its low calorific value and high ash content. After these processes, the huge amount of tailings is produced from the plants, and they must be dewatered before disposal. For this purpose, flocculation is a widely preferred method for solid-liquid separation of fine coal tailings. In this method, long-chain polymers are used to bind particles together to form bigger particles to settle them easier and faster. Flocculation process is affected by various parameters including solid ratio, pH, temperature, stirring speed and time, molecular weight, chain length, charge, and dosage of flocculant. In the flocculation process, flocs with several physical characteristics such as size, structure, and strength are formed depending on these flocculation conditions. Different floc characteristics are preferred for various processes. For example, strong and high-density flocs are favorable in filtration, but not in sedimentation processes. Therefore, it is extremely important to characterize the flocs to optimize the flocculation processes [1-7]. For this reason, there have been various studies on the investigation of floc size, density, structure, and strength [8-13]. Different techniques were used for the floc strength measurements such as image-based tech-Article History:

The amenability of gold nanoparticles (AuNPs) coating on natural and modified (hexadecyl trimethyl ammonium bromide, CTAB) sepiolite surfaces was studied both experimentally and theoretically. The zeta potential experiments and Fourier transform infrared spectrophotometer (FTIR), environmental scanning electron microscope (ESEM), and transmission electron microscopy (TEM) analyses were carried out with the sepiolite samples in the presence of AuNPs. In addition, the adsorption of three gold-nanoparticles on the sepiolite surface (100) in the absence and presence of CTAB was investigated by molecular dynamics (MD) simulations. The AuNPs showed no significant change in the zeta potential of natural sepiolite surfaces due to negative charges of both the sepiolite and AuNPs at natural pH. The surface charge of modified sepiolite decreased with the increase in AuNPs concentration indicating the significance AuNPs adsorption. FTIR, ESEM, and TEM analyses indicated the coating of AuNPs onto the modified sepiolite surface were higher than that of the natural sepiolite surface. The MD simulation results showed that AuNPs can easily adsorb onto the basal surface of the sepiolite due to its hydrophilicity in the presence and absence of CTAB as indicated in the experimental studies. In short, the modification of sepiolite with CTAB made the charge positive, and in turn considerably increased the AuNPs coating on sepiolite surfaces due to electrostatic attraction.