Previous studies of agave bagasse (AGB-byproduct of tequila industry) presented unidentified crystalline peaks that are not typical from common biofuel feedstocks (e.g sugarcane bagasse, switchgrass or corn stover) making it an important issue to be addressed for future biorefinery applications. Ionic liquid (IL) pretreatment of AGB was performed using 1-ethyl-3-methylimidazolium acetate ([C(2)mim][OAc]) at 120, 140 and 160 degrees C for 3 h and a mass fraction of 3% in order to identify these peaks. Pretreated samples were analyzed by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electronic microscopy (FE-SEM), thermal analysis (TGA-DSC) and wet chemistry methods. Previous unidentified XRD peaks on AGB at 2 theta = 15 degrees, 24.5 degrees and 30.5 degrees, were found to correspond to calcium oxalate (CaC2O4) in a monohydrated form. IL pretreatment with [C(2)mim][OAc]] was observed to remove CaC2O4 and decrease cellulose crystallinity. At 140 degrees C, IL pretreatment significantly enhances enzymatic kinetics and leads to similar to 8 times increase in sugar yield (6.66 kg m(-3)) when compared to the untreated samples (960 g m(-3)). These results indicate that IL pretreatment can effectively process lignocellulosic biomass with high levels of CaC2O4. (C) 2015 Elsevier Ltd. All rights reserved.