Nitric Acid Oxidation for Improvement of a Chinese Lignite as Soil Conditioner

Abstract

Oxidation is known commonly to enhance humic acid (HAs) contents of coal, but in China, most humic substances are used directly as soil conditioners or applied in combination with fertilizers without oxidation. Therefore, we investigated the impact of nitric acid (HNO 3 ) oxidation on the characteristics of HAs derived from a Chinese lignite. The results showed that total HA content was increased by HNO 3 oxidation, thus consequently increasing its cation exchange capacity and moderate humification. Besides, HAs extracted from oxidized lignite were richer in oxygen-containing functional groups with smaller molecular size than natural lignite. Compared with natural lignite, retention capacities of nitrogen and potassium by oxidized lignite were significantly greater. However, phosphorus-retention capacity was decreased to near zero, which might enhance the availability of phosphorus in soil. In general, optimum HNO 3 oxidation had favorable effects on lignite and improved its characteristics for use as a soil conditioner.

Phosphogypsum amendments and irrigation with acidulated water affect tomato nutrition in reclaimed marsh soils from SW Spain

“…This can also contribute to increase the absorption by plants of other micronutrients adsorbed on Fe oxides, such as Zn (Montilla et al, 2003), Cu (Bibak, 1997), or B (Goldberg & Glaubig, 1986). Also, the nitric acid treatment can oxidize soil organic matter thus releasing metal bound to it (Tessier et al, 1979) or can alter the structure of organic matter (Liu et al, 2011) increasing its complexing capacity, which can positively affect the availability of metallic elements to plants (de Santiago & Delgado, 2007). The decreased concentration in fruits and the decreased total content in aerial parts of K with the nitric acid application could be the result of an antagonism with Ca because the application of acid promotes the dissolution of Ca-carbonates and thus increases Ca activity in soil solution.…”

Low-Rank Coal as a Source of Humic Substances for Soil Amendment and Fertility Management

“…Oxidation may enhance the HA content of coal sources to be used as soil conditioners. Two independent experimental studies showed that nitric acid (HNO 3 ) oxidation of brown coal leads to the increase of HA content with richer functional groups and ensures the retention rate of nutrients, which consequently improves soil aggregate stability and associated structure [52,53].…”

“…The high content of TOC and its relatively slow mineralization suggest LRC be attractive for increasing plant nutrient supply in the soil the same way as known organo-mineral fertilizers [52]. The application of LRC by B. Dębska with colleagues [21] resulted in an increase in TOC content (by ~300%) and elevated soil organic carbon with higher aromaticity (38.6% compared to 35.4% in controls), which implies higher C sequestration potential and recalcitrance.…”

Ruthenium ion catalytic oxidation depolymerization of lignite under ultra-low dosage of RuCl3 catalyst and separation of the organic products with inorganic salts

“…Extraction of lignite with organic solvent CS 2 shows that lignite is also rich in aliphatic hydrocarbon structure, which also provides the possibility of its degradation into small molecular fatty acids. 10 There are many oxidation methods for the preparation of carboxyl chemicals by oxidation depolymerization, such as alkali-oxygen oxidation, 11 sodium hypochlorite oxidation, 13,14 nitric acid oxidation, 15 catalytic O 2 oxidation, 16 H 2 O 2 oxidation, 17,18 ruthenium ion catalytic oxidation, [22][23][24][25] etc. Alkali-oxygen oxidation method can obtain various small molecular fatty acids and BPCAs.…”