Characteristics and elementary composition of cotton stalk-char in different carbonization temperature and time

Abstract: In order to reveal the influences of carbonizing temperature (300℃, 450℃, 600℃) and time (0.5 h, 1 h, 2 h, 4 h, 6 h) on the characteristics and compositions of biochar, we studied the characteristics of biochar, such as pH, Cation Exchange Capacity (CEC), EC,etc. and both element composition, such as organic carbon, nitrogen and mineral element contents, and their relationships with cotton stalk-char made by the cotton stalk. The results showed that (1) the ratio of carbon of stalk, organic carbon content of cotton stalk-char decreased with the carbonization temperature and time increasing (the ratio of cotton stalk-char of cotton stalk: 48.66% (300℃) >35.39%(450℃)>31.06%(600℃). With the time extended, the pH value of the cotton stalk-char was increased below 300℃, and it kept around 10.5 at 450℃ and 600℃. The EC increased with the carbonization temperature increasing, and its change was not obvious in carbonization time. The carbonization temperature between 300℃ and 450℃ imposed less on EC, but at 600℃ the imposition was enormous. The CEC of the cotton stalk-char decreased with the carbonization temperature increasing. Its value increased at 300℃ with the carbonization time extended, however, this trend disappeared at 450℃ and 600℃. (2) The contents of total phosphorus(TP), total potassium(TK), available potassium(AK), calcium(Ca) and magnesium(Mg) in cotton stalk-char were increased with the carbonization temperature increasing and time extending, but the total nitrogen(TN) and alkaline nitrogen(AN) were negative, and the changing tendency was 90.07 mg/kg(450℃)>60.72 mg/kg(600℃)>20.18 mg/kg(300℃) for available phosphorus (AP). (3) The correlations among carbonization temperature, time and indicators of cotton stalk-char showed that it was negative between carbonization temperature or carbonization time and the ratio of carbon, cotton stalk, CEC, organic carbon, TN , AN of cotton stalk-char, and to the pH value, TP, TK,AP AK, Ca and Mg, they are positive. Above all, the cotton stalk-char carbonized by the lower temperature and shorter time (300℃, 1-2 h) could be the better expected choice for an agricultural application. These results could supply some support for the production of biochar and utilize cotton stalk originated in Xinjiang.