The present invention discloses a method for ammonium-enhanced flue gas desulfurization (FGD) by using red mud slurry. The method specifically includes: crushing red mud, sieving the crushed red mud, slurrying the red mud, conducting aeration treatment, adding an ammonium salt and/or ammonia, and conducting natural sedimentation to obtain pretreated red mud slurry and pretreated red mud liquor; adding an ammonium salt and/or ammonia to the slurry, adding water and conducting uniform mixing, conducting pre-FGD, conducting deep desulfurization on treated flue gas by using the pretreated red mud liquor, and directly discharging desulfurized flue gas; and charging the pretreated red mud slurry and the pretreated red mud liquor obtained after the treatment to a replacement tank below, adding lime milk to the replacement tank, conducting stirring and natural sedimentation, conducting soilization on subnatant thick red mud slurry, and refluxing the supernatant to a red mud aeration tank.

The present invention discloses a method for ammonium-enhanced flue gas desulfurization (FGD) by using red mud slurry. The method specifically includes: crushing red mud, sieving the crushed red mud, slurrying the red mud, conducting aeration treatment, adding an ammonium salt and/or ammonia, and conducting natural sedimentation to obtain pretreated red mud slurry and pretreated red mud liquor; adding an ammonium salt and/or ammonia to the slurry, adding water and conducting uniform mixing, conducting pre-FGD, conducting deep desulfurization on treated flue gas by using the pretreated red mud liquor, and directly discharging desulfurized flue gas; and charging the pretreated red mud slurry and the pretreated red mud liquor obtained after the treatment to a replacement tank below, adding lime milk to the replacement tank, conducting stirring and natural sedimentation, conducting soilization on subnatant thick red mud slurry, and refluxing the supernatant to a red mud aeration tank.

An apparatus for the layer-by-layer formation of three-dimensional objects, the apparatus comprising a gas extraction system and an enclosed working space from which gas is to be extracted, wherein the working space is enclosed by side walls, a ceiling and a working surface, and comprises a working space inlet for allowing gas to enter into the working space, a working space outlet for allowing gas to exit the working space, and a build bed surface in which a layer of the object is formed; wherein the gas extraction system comprises: a primary conduit comprising at least a first primary inlet, at least a first interfacing inlet, and a primary outlet; and at least a first secondary conduit comprising a respective first secondary inlet and a respective first secondary outlet, the first secondary inlet being in fluidic communication with the working space for extracting gas from the working space, and the first secondary outlet being in fluidic communication with the first interfacing inlet; wherein the or each primary inlet is open to an environment external to the working space, and wherein the primary outlet is connectable to an external extraction source so as to suction gas from the primary conduit; and wherein the gas extraction system further comprises one or more flow control devices for controlling the flow of gas from the working space into the first secondary conduit, and thence into the primary outlet of the primary conduit. Methods for operating the apparatus, and a controller for controlling the apparatus and carrying out the methods, are also provided.