Abstract: A slurry of contaminated sand and water is delivered to a solid/liquid hydrocyclone (2) surmounting a pressure vessel (1). That is divided into two sections (3, 4) by a bulkhead (5) leaving a gap between the sections at the top. The partially cleaned sand from the hydrocyclone (2) is dropped into one section (3) while the water is directed to the section (4). The sand is then fluidized with clean, preferably recycled water and directed back through the hydrocyclone (2). This is repeated several times, progressively cleaning the sand. Oil removed by the process floats on the water in the section (4) and is discharged to drain (22). Provision for degassing the pressure vessel (1), discharging the fully cleaned sand, and for flushing and draining the pressure vessel is made.