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This work aims to develop new uses for sewage sludge, which is a byproduct of municipal wastewater treatment plants, by examining the calcination of this waste, the characterization of ashes is obtained, and its use to prepare desulfurant sorbents. Samples of sewage sludge were obtained from a local municipal wastewater treatment plant. This plant applies a pre-treatment followed by a biological treatment, where anaerobic digestion and centrifugation reduces the sludge. Three samples were characterized (in humidity, volatile and fixed solids content), dried, and ignited at two temperatures, 550 and 750°C. The composition of the ash obtained at both ignition temperatures was studied by x-ray fluorescent spectroscopy and the BET specific surface area of the two ashes and of the prepared sorbents was measured. Ash composition was similar for the two temperatures tested, where the components were Si, Ca, Al, Fe, P, S, Mg, K, Cl, Zn and Ti. BET specific surface area values indicate that the lower temperature of calcination produces ash with the highest SSA values (18 m2/g against near 10 m2/g). Preparation of desulfurant sorbents was carried out by mixing the ash with CaO or Ca(OH)2 at room temperature and different experimental conditions. The BET SSA of the prepared desulfurant sorbents showed higher values for the sorbents prepared with the ashes obtained at the lowest temperature. The behaviour of the ash and the prepared sorbents was tested in a fixed bed reactor at 58°C with a flue gas containing 5000 ppm of SO2 with a relative humidity of 55%. Results in the desulfurization process show that the calcium from the sludge seems more efficient than the calcium added as CaO or Ca(OH)2 to prepare the sorbents.

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Several calcium-hydroxide-based sorbents were prepared by mixing commercial Ca(OH) 2 and a magnesic smectite using two lignosulfonates (LGSs) as additives, and their structural and desulfurant properties were studied. The sorbents were characterized using scanning electron microscopy (SEM) with an X-ray detector and N 2 adsorption techniques. The dry desulfurization activity at a low temperature was investigated in laboratory-scale equipment. When LGSs are used in low amounts, their dispersant or deagglomerating properties observed by SEM produce an increase in the porosity and specific surface area (SSA) with respect to the sorbent prepared without LGSs. Their desulfurization activity increases up to 71% with respect to the solid prepared without additive, with the increase in the porosity and SSA values being the main factor to explain the higher SO 2 retention values but also their hygroscopic properties. The composition of the spent sorbents allows to use them as soil amendment. The use of these LGSs in the preparation of calcium-based sorbents is an excellent and easy way to improve their desulfurant behavior, with an easy preparation at ambient temperature, and it is also another promising option to valorize this lignocellulosic waste.