Effects Of Low Molecular Weight Organic Acids On Phosphorus Fixation By Calcite

Calcite is a commonly mineral found in calcareous soil,which can fix phosphorus and affect the environmental geochemical cycle of phosphorus.Low-molecular-weight organic carboxylic acid is a common product secreted by plants in the soil and has a certain effect on the interaction between phosphorus and soil minerals.In nature,organic acids,phosphorus,and calcite often coexist,but there are few studies on phosphorus fixation by calcite under the coexistence of organic acids.Therefore,in the coexistence system of calcite,organic acid,and phosphorus,it is of practical significance to study the migration and transformation laws of phosphorus.Through the batch equilibrium method,combining the p H conditions,reaction time,types of organic acids,and concentration,the fixation of phosphorus on calcite was studied.???The interaction between calcite and phosphorus showed that:At p H7.7,P removal was mainly by adsorption at initial P concentration?2.2 mg?L^-1,with dominant precipitation occurring at initial P concentration?3 mg?L^-1;At p H8.3,adsorption was the key removal process at initial P concentration?7.5 mg?L^-1,whereas precipitation was observed at initial P concentration of 10 mg?L^-1;At p H 9.1 and 10.1,P removal mechanism was mainly by adsorption at initial P concentration?10 mg?L^-1.Combined with the kinetic results,when the SI_ACP value is between 1.97 and 2.19(SI_OCP between 1.99 and 2.32)in the 24 h reaction time,phosphorus will precipitate.???The interaction between calcite and organic acids showed that:?1?The adsorption of malic acid,tartaric acid,and citric acid increased first and then slowed down with time.Under different p H conditions,the time to reach adsorption equilibrium was different;?2?As the p H increased?7.7 to 9.7?,the electronegative effects on the surface of calcite and the competition effects of HCO₃^-and CO₃^2-in the solution increased,leading to a continuous decline in the adsorption of all three organic acids;?3?At different temperatures,the adsorption of three organic acids on calcite was more in line with the Langmuir model,and the temperature increase was favorable for their adsorption.???The effect of organic acids on phosphorus fixation by calcite showed that:?1?malic acid can reduce the removal of phosphorus and delay the occurrence of precipitation through adsorption competition and complexation with Ca²⁺in solution;?2?tartaric acid can reduce the removal of phosphorus,or even delay the occurrence of precipitation through competitive action,complexation and free precipitation;?3?citric acid can reduce the removal of phosphorus and delay the time of precipitation mainly through competitive action and complexation.In this study,three low molecular weight organic carboxylic acids were selected as the measuring factors.By studying the effects of different concentrations and types of organic acids on phosphorus fixation by calcite,it provides a theoretical basis for studying the effects of other low molecular weight organic acids on the relationship between phosphorus and soil minerals.