| Weathered coal,a kind of shallow coal exposed to the surface or below the surface,has great utilization value for agriculture because it is rich in humic acid.However,the weathered coal resource has not been effectively used due to low extraction rate of humic acid.Therefore,this study was carried out to analyze the characteristics of weathered coal from different sources and classify the weathered coal with different properties,develop processes and protocols for humic acid?HA?activation and extraction suitable for different types of the weathered coal.Meanwhile,the biological activity of Humic acid biostimulant?HABS?from different sources of the weathered coal was determined in order to provide a theoretical basis for the efficient utilization of humic acid in weathered coal.In this experiment,11 kinds of weathered coal from different sources in Shanxi Province were collected for classification and investigation.The research results are as follows:1.Wide variation in humic acid content and calcium and magnesium composition was found in the weathered coal from different sources.According to the ratio of free humic acid to total humic acid in weathered coal?F/T value?,11 kinds of weathered coal were divided into four grades:F/T< 10%,F/T between 10 % and 50%,F/T between 50 % and 90 %,and F/T> 90 %.The content of calcium and magnesium had a significant negative correlation with the free humic acid content,and also highly significant negative correlation with the value of F/T of the weathered coal.In other words,the higher the content of calcium and magnesium in weathered coal,the lower the value of F/T.Therefore,calcium and magnesium ions are the key limiting factor responsible for the low humic acid extraction rate of the weathered coal with high calcium and magnesium content.2.Weathered coal samples No.1?F/T<10 %?,No.5?F/T between10 % and 50%?and No.7?F/T between 50 % and 90%?with F/T less than90 % were selected for activation treatment by using NH4HCO3 and?NH4?2HPO4 as activators.The two activators improved the free humic acid content of the three weathered coal samples.The types,dosage and process of activators varied depending on coal samples.As sample F/T value increased,the activation became more difficult.Higher activation rate could be achieved for the weathered coal with a small F/T value even when reactively low rate of single activator was used.However,the weathered coal with a large F/T value could obtain a higher activation rate only when combination of two activators was used.In addition,chemical activation causes the change in the chemical structure and surface physical structure of weathered coal,and could significantly reduce the exchangeable calcium and magnesium content in the weathered coal.3.Research was conducted on humic acid extraction techniques of different kinds of the weathered coal.The results showed that the optimum conditions and techniques for humic acid extraction varied depending on sources of the weathered coal.KOH concentration is the main factor determining the extraction rate of humic acid.The higher the content of free humic acid in weathered coal,the greater the KOH concentration required for extraction.The optimal KOH concentration for No.10 weathered coal?free humic acid content =41.07 %?was 2.5 %,while that for No.11 weathered coal?free humic acid content =26.10 %?was 1.5 % only.The extraction temperature and time had less effect on the extraction rate.However,under the same conditions,the lower the free humic acid content in the weathered coal,the greater the temperature and time was required.The optimum extraction temperature and time for No.10 weathered coal were 40 ? and 30 min,respectively,whereas those for No.11 weathered coal were 50 ? and45 min,respectively.4.The humic acid solution obtained through optimum activation and extraction processes from different types of weathered coal was further purified to produce humic acid biostimulant?HABS?.The rootless mungbean seedlings were treated with HABS,and the biological activity of HABS was evaluated based on root length,root weight,root surface area,root diameter,and number of root tips of the newly developed roots from the seedlings.IAA served as the positive control.The results showed that different HABS could promote the re-rooting of the mungbean.HABS of the No.7 weathered coal had better biological activity at a lower concentration of 0.05 %.It had the best biological activity among the weathered coal samples and greater promoting effects on the root system when compared to the IAA at the optimum rate?2.50 ?g/m L?. |
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