Process for the preparation of an aqueous tar suspoemulsion by mixing a mixture comprising: (a) a viscous tar composition formed from a tar, from inorganic solids and, optionally, from water; (b) water (W); (c) a surface-active agent (SA) exhibiting an HLB of at least 10 and, optionally, (d) a thickening water-soluble polymer (TWP) with a molecular mass of greater than 10,000, the relative amounts of constituents (W), (SA) and, optionally, (TWP) being such that the viscosity of the (W) + (SA) + optional (TWP) mixture is preferably equal to or greater than the viscosity of the said tar, and then optional dilution of the mixture obtained with water or with an aqueous acidic solution. Application to the residues, containing sulphuric acid, resulting from the synthesis of white oils from petroleum fractions. The present invention further relates to a method for fluidizing acidic tars/sludges comprising contacting the tar/sludge with sulphuric acid and a surfactant. Optionally, a carrier for the surfactant's incorporation into the tar/sludge can be utilized. This provides an effective process for cleaning sulphuric acid tars/sludges from containers/vessels such as transportation containers, pipes and storage tanks. Preferably, the process comprises the additional step of regeneration of sulphuric acid from the fluidized tar/sludge.