Formation Of Insoluble Phosphate Research Articles

Enhanced Fe-bound phosphate availability by the combined use of Mg-modified biochar and phosphate-solubilizing bacteria

The formation of insoluble phosphate in soils and resulting overfertilization causes a large environmental risk. Although phosphate-solubilizing bacteria (PSB) can solubilize Ca-bound phosphate well by acidification, they often have a low capacity to solubilize Fe-bound phosphate (Fe-P). In this study, a novel Mg-modified lignin biochar (MB) was prepared via the chemical impregnation method to improve the ability of PSB to dissolve FePO4. The results show that dissolved phosphate rapidly increased to approximately 0.9 mM over 3 days in the FePO4 + PSB + MB system. The system with MB was more effective to increase FePO4 dissolution by 17 times and increase the amount of organic acids production by 2 times than that without the MB. The characterization results indicated that the polymerization and rearrangement of FePO4 occurred when the FePO4 particles attached to the surface of the MB, resulting in the formation of Fe(III)2Fe(II)(P2O7)2 crystals on the surface of the MB. The Mg on the surface of the MB can induce the preferential orientation of the [210] crystal plane of the Fe(III)2Fe(II)(P2O7)2, which can be preferentially dissolved by PSB, causing an increase in Fe-P solubility. This study provides a new method for the development of insoluble phosphate solubilization technology to limit the overfertilization of soil and offers a clear understanding of the interactions among biochar, Fe-P, and PSB.

Influence of irrigation with microalgae-treated biogas slurry on agronomic trait, nutritional quality, oxidation resistance, and nitrate and heavy metal residues in Chinese cabbage

Biogas slurry (BS) is a main byproduct of biogas production that is commonly used for agricultural irrigation because of its abundant nutrients and microelements. However, direct application of BS may cause quality decline and nitrate and heavy metal accumulation in crops. To address this issue, a microalgae culture experiment and an irrigation experiment were performed to evaluate the removal efficiencies of nutrients and heavy metals from diluted BS by microalgae Scenedesmus sp. and to investigate the effects of irrigation with microalgae-treated BS (MBS-25, MBS-50, MBS-75, and MBS-100) on nutritional quality, oxidation resistance, and nitrate and heavy metal residues in Chinese cabbage. After 8 days of continuous culture, a ratio of 1/1 for BS/tap water mixture (BS-50) was the optimal proportion for microalgal growth (3.73 g dry cell L−1) and efficient removal of total nitrogen (86.1%), total phosphorus (94.3%), COD (87.5%), Cr (50%), Pb (60.7%), and Cd (59.7%). The pH in MBS-50 medium recovered to the highest level in a shorter period of time and accelerated the gas stripping of ammonia nitrogen and the formation of insoluble phosphate and metals, which partly contributed to the high removal efficiencies. MBS irrigation significantly promoted crop growth; improved nutritional quality, edible taste, and oxidation resistance; and reduced nitrate and heavy metal residues in Chinese cabbage at a large scale. Therefore, microalgae culture was beneficial to reduce negative impacts of BS irrigation in crop growth and agricultural product safety. This study may provide a theoretical basis for the safe utilization of BS waste in agricultural irrigation.

Activated carbons from bituminous coals by reaction with H 3PO 4: The influence of coal cleaning

A study has been made to examine the effects of coal cleaning by column flotation on the properties of carbons prepared by the phosphoric acid activation of bituminous coals. Earlier work has shown that while moderate surface areas are generated by the reaction of coals with H 3PO 4 at temperatures around 550°C, phosphoric acid also reacts with coal sulfur and mineral matter. These side reactions consume reagent that is otherwise available for reaction with the organic structure, and result in the formation of insoluble phosphates, increasing the carbon ash content and limiting the amount of recoverable reagent. Lowering the mineral matter content of the coals prior to carbon synthesis is found to have a direct influence on reducing the ash content of the derived carbons and the extent of phosphorus retention. Coal cleaning also increases the extent of sulfur removal (most of which is liberated as H 2S), the BET and mesopore surface areas, and the carbon pore volume. Possible causes of these effects are discussed. The assumption that the ash in the carbon has negligible porosity, and hence that the reduction in mineral matter content of the coal will automatically increase the specific surface area of the carbon by lowering the ash content, does not appear to fully explain the results. The consumption of phosphoric acid by side reactions lowers the effective reagent to coal ratio and limits the amount of available reagent, which can cause a reduction in surface area. Further, it is possible that ash constituents can block the pore structure, and that lowering the coal mineral matter content will improve access. It seems probable that all three explanations have some validity and can contribute to the observed changes.

Ion exchange in fused salts : I. Chromatographic behaviour of various metal cations in fused salts on γ-alumina and synthetic inorganic ion exchange materials

The chromatographic adsorption on γ-alumina and synthetic inorganic ion exchange materials of various metal cations dissolved in a fused lithium nitrate—potassium nitrate eutectic was studied. The results obtained seem to confirm that metal ions are adsorbed by ion exchange, although other mechanisms, e.g. oxide precipitation, or formation of insoluble phosphates, are possible. A relationship between the adsorption of the metal ions tested, the solubility of their oxides and the ionic potentials was found. Some conflicting results of other authors are discussed.