diluted and subjected to a second filtering step at 60 this dilution and subsequent filtering is to remove soluble salts which may have increased to an objectionable quantity the amount of the filter cake which is diverted to the dilution step can vary but when it is applied it is ordinarily of the order of 50 the filter cakes from the two filtrations then represent the kaolin slurry which is fed to the spray dryer as seen in fig1 although only one spray dryer is illustrated several spray dryers as previously mentioned can be employed in tandem and the gases from several e g two of them can be fed to the scrubber in accordance with the invention the heated water issuing from the scrubber is primarily employed in connection with the filtering operation although it can also be employed for other purposes as will be described hereinafter its application for filtering is of particular importance because it materially facilitates the filtering as well as supplying heat to the slurry which will eventually be fed to the spray dryer and thus require less heat input to remove its water content referring again to fig4 the heated water from the scrubber 25 line 38 is supplied to a heat exchanger 62 through which the crude suspension after having been subjected to the classifying step is passed this raises the temperature of the suspension materially as it is fed to the bleaching and filtering step 59 the heated water from line 38 enters through line 64 and leaves heat exchanger 62 through line 66 which returns it to water inlet line 32 of the scrubber so that a complete circuit is made the water produced by.