POINT OF ZERO CHARGE DETERMINATION OF TEN STANDARD BIOCHARS FOR THE REMOVAL OF METHYLENE BLUE FROM AQUEOUS SOLUTIONS

摘要

This study describes the determination of the point of zero charge (PZC) of ten standard biochars (BC), supplied by the UK Biochar Research Centre (UKBRC), using the salt addition method, in order to select suitable biochar(s) for methylene blue removal from aqueous solutions. The initial pH (pHi) was adjusted in a range of 3 to 13 using NaOH and HNO_3 solutions. The experiments employed a biochar dose of 10 g L~(-1). The final pH values (pH_f) were recorded in the remaining suspensions after a 24-hour contact time at 120 rpm. The difference between pHi and pH_f (ApH) was plotted against pHi values and the pH at PZC (pH_(PZC) corresponded to the point of intersection in the resulting curve. The results obtained in 0.1 mol L~(-1) NaNO_3 were the following: PZC at 7.24 and 8.53 for rice husk biochar (RH), the first obtained at 550 °C pyrolytic temperature and the latter at 700 °C (RH550 and RH700); PZC at 8.81 and 9.46 for oil seed rape straw pellets biochar obtained at 550 °C and 700 °C (OSR550 and OSR700), respectively; PZC at 9.24 and 9.84 for wheat straw pellets biochar (WS550 and WS700, respectively); PZC at 8.98 and 8.94 for Miscanthus straw pellets biochar (MSP550 and MSP700, respectively); and PZC at 6.73 and 7.15 for soft wood pellets biochar (SWP550 and SWP700, respectively).