A process for cooling and purifying a hot gas containing slag particles comprises the following steps:(a) the velocity of the gas mixture is reduced;(b) the flow of the gas mixture having a reduced velocity is deflected, the gas mixture being passed upward in substantially vertical direction so that part of the slag particles falls down into a fluidized bed of slag particles;(c) cold clean recycle gas is introduced through a fluidization distributor into the fluidized bed, thereby cooling the slag particles and keeping at least part of the slag particles in the fluidized bed;(d) the gas mixture flowing substantially vertically upward at reduced velocity is cooled by indirect exchange of heat, while a further quantity of slag particles falls down into the fluidized bed; and(e) the cooled slag particles are discharged from the bottom of the fluidized bed through a discharge pipe.An apparatus to carry out this procedure is also described.