Pyrite was removed from Illinois #6 coal by HF/HCl washes and by CrCl2 reduction. The effect of pyrite on the coprocessing of Illinois #6 coal with waste automotive oil was investigated. ICP results show that the standard HF/HCl treatment still leaves about 65% of the pyrite in the Illinois #6 coal, but acidic CrCl2 reduction can remove 95.9% of the pyrite from the same coal without causing significant alteration of the organic matter as shown by examination of samples before and after treatment by infrared and C-13 NMR spectroscopy as well as by atomic ratios (H/C, N/C and S-organic/C). XPS results show that compared to untreated Illinois #6 coal, the inorganic composition on the surface of CrCl2 treated Illinois #6 coal changes very little except for loss of pyrite, whereas the inorganic composition of HF/HCl treated Illinois #6 coal changes substantially. A comparison between untreated coal and CrCl2 treated Illinois # 6 coal was made by TOF-SIMS (Time-of-Flight Secondary-Ion Mass Spectroscopy). Nearly total removal of pyrite from Illinois #6 coal by CrCl2 decreases the conversion yield of the coal to THF solubles to 16.2%, compared to 60.9% for untreated Illinois #6 coal and 53.4% for HF/HCl treated Illinois #6 when each of these coals is coprocessed with waste automotive oil under the same reaction conditions. This comparison of conversion yields of the coal further supports the conclusion reached previously that pyrite functions as a catalyst aiding in dissolution of the coal to form gas, oil, asphaltenes and char.