Effects Of Typical Low Molecular Weight Organic Acids On The Adsorption Of Pb(?) Via Humin

Low molecular weight organic acids are important components of root exudates.They not only participate in the life activities of plants and microorganisms in the soil,but also have an important impact on the adsorption and desorption behavior of heavy metals in the soil.Humin is a highly efficient heavy metal adsorbent especially has good effect to Pb,Cd and Cu in soil,according to some references.Therefore,it is especially important to study the behavior and mechanism of small molecule organic acids on the adsorption of heavy metals by humin.In this paper,the effects of tartaric acid,succinic acid and lactic acid on the adsorption of lead by humin in aqueous solution and its mechanism were studied.The conclusions are as follows:?1?The humin was extracted from peat soil by alkaline extraction.From the characterization results,it can be seen that humin is an irregularly shaped substance with a large number of oxygen-containing functional groups such as hydroxyl and carboxyl groups on the surface and the measured specific surface area is 19.19m²?g^-1.Under the influence of three organic acids of 0.1mmol?L^-1,the adsorption of lead ions by humin was followed by pseudo-second-order kinetics model and Langmuir model,which is monolayer adsorption.The adsorption process began with external rapid chemical adsorption followed by a slow internal diffusion of lead ions.?2?Considering tartaric acid as the representative,the effect of tartaric acid on the adsorption of lead by humin was studied when 0.1mmol?L^-1 tartaric acid was added.The results showed that the effect of tartaric acid on adsorption was related to the concentration of tartaric acid.With the increasing of tartaric acid concentration,the adsorption of lead ion by humin showed a peak change and the adsorption amount reached the maximum at 0.5mmol?L^-1.It own to the low concentration of tartaric acid(less than 0.5mmol?L^-1).The oxygenated groups contained in tartaric acid itself can be combined with humin by hydrogen bonding,which is equivalent to increasing the carboxyl group on the surface of humin,thus adsorption amount was increased.The increasing of the concentration of tartaric acid leads to an increment of free tartaric acid in the solution,which will complex with the lead ions in the solution,and indirectly reduce the amount of lead ion adsorption on the humin.?3?Supplementary adsorption study of succinic acid?2 carboxyl groups?and lactic acid?1 carboxyl group and 1 hydroxyl group?were carried out,comparing with tartaric acid.From the difference in functional groups among tartaric acid?2 carboxyl groups and 2 hydroxyl groups?,succinic acid and lactic acid,it can be found that the amount of lead ions adsorbed by humin in the presence of these three acids is in the following:succinic acid>tartaric acid>lactic acid.This indicated that the dibasic acid has a greater influence on the adsorption than the monobasic acid.