Materials All reagents were of the highest quality available. Hydrogen peroxide (30% [w/w] H2O2 in water) solution and mannitol were purchased from Sigma (St. Louis, MO), and FeCl2·4H2O (99%) was obtained from Fluka. All solutions were prepared with Millipore-quality water (Milli-Q plus, Ultrapure water system, 18 MΩ·cm). Residual Kraft Black Liquor Residual Kraft black liquor was kindly provided by Smurfit-Mocarpel pulp mill (Venezuela). This black liquor is derived from the digestion of Caribbean pine (Pinus caribaea) and was taken from the recovery plant at the process line, where the total solid content was 32.7%, density was 1.2 g/mL,