Study On Extraction And Microbial Degradation Of Humic Acid From Zhaotong Brown Coal

Zhaotong lignite is the largest lignite field in southern China, the region total reserves of about 8.1 billion tons, accounting for 51.8%of lignite resources in Yunnan province. Due to its high content of moisture and ash, low calorific value, and stablility is poor, the conventional technologies, gasification, combustion, and so on, are not suitable for Zhaotong lignite. However, using it to extracted humic acid would be a viable and sustainable process, because of its high content of humic acid.In this paper, the study emphasis was focused on two aspects. First, humic acid extractiong from Zhaotong lignite, in this field the effects of different process conditions on humic acid extraction yield and quality were investigated. Second, microbial degradation characteristics of humic acid fron Zhaotong lignite were studied. After above research, we can provide basic data for the comprehensive utilization of Zhaotong lignite. The results are as follows:(1) Under the condition of alkali concentration 1.5%, reaction temperature 80℃ and reaction time 3h, Zhaotong lignite had the maximum humic acid extraction yield, an in the study pH ranger, the smaller the acid precipitation, the higher humic acid extraction yield was. Along with the increasing of extraction pressure the yield of humic acid increased.(2) Proximate analysis of the humic acid under different process conditions was as followed:ash content 7.77-18%, volatile matter content 37.33-45.33%, fixed carbon content 32.73～45.74%, which showed that a certain content of ash still existed in humic acid products. Determination of acidic functional groups indicated that the change of acidic functional groups content of humic acid under different extraction conditions is not strong regularity, total acidic group content of humic acid in the range of 3670-2980cm-1 belong to the polymer fat or aromatic-OH associated with hydrogen bond; 2920-2850cm-1 is an aliphatic C-H stretching vibration. There is no absorption vibration and absorption peak in the frequency range of 2770-1778cm-1; all the peak of carboxyl absorption of humic acid products had appearance of red shifting, which shift to 1640cm-1.(3) Metal element measurements and XRD diffraction characterization of Zhaotong lignite, humic acid product and extraction residue indicated that Ca, Mg, Al, Fe, Si and other metal element were the main components in the ashes of above lignite, humic acid product and extraction residue. The main elements forms of the aboved metal elements were silicate, aluminum silicate oxide, hydroxide alone or in a mixed form.(4) By comparing the humic acid extraction yield of Zhaotong, Xiaolongtan and Xianfeng lignite, under the optimal conditions:alkali concentration 1.5%, extracting temperature 80℃ and extracting time 3h, the extraction yield was Zhaotong lignite 69.89%, Xiaolongtan 40.9%and Xianfeng lignite 40.13%, respectively. After pickling pretreatment of lignite, the extraction yield of above mentioned lignite were 76.13%, 47.61%and 43.48%, respectively. Extraction yield of Zhaotong lignite humic acid is much higher than the others. From FTIR spectra of above three lignite and humic acid, we can be found that humic acid product characteristic infrared peak position and peak shape is very consistent, and that humic acid from different sources is in common.(5) By comparing the effects of humic acid transformation and microbial growth in bacteria inorganic salt medium and czapek liquid medium, humic acid microbial transformation occurred only in bacterial environment.(6) It can be concluded from the microbial degradation experiment, that microbial transformation of Zhaotong lignite humic acid can take place to product fulvicacid, and the yield was 7-25%, and the growth of the microorganisms was visible. After microbial transformation and degradation, the absorbance E4/E6 value and cohesion limit values of humic acid generally increased, which proved that the molecular weight of humic acid has been reduced.(7) By comparing the effects of the mud river mud microbe and soil microbe, it could found that river mud microorganisms had the ability to degrade humic acid, but compared with the soil microbe, river mud microbial adaptation capability was weak.(8) Compared with microbial conversion and microbial growth of Zhaotong lignite humic acid, the microbial effects on BHA fertilizers and scraps were not obvious, which proved indirectly that Zhaotong lignite humic acid in soil was more prone to conversion degradation.