盐酸四环素(TCH)被广泛应用于医疗、畜牧养殖和农业等行业中,但由于在使用过程中不能被人和动物完全吸收,而是随粪便与尿液排泄进入环境水体,而TCH会破坏生态环境、危害人体健康、催生耐药毒菌,对环境和人体健康造成威胁,因此找到一种经济高效的去除方法对于水质安全非常重要.目前,水中TCH的去除方法主要包括化学法、生物法和物理法,相对于化学与生物处理法,物理法中的吸附法去除污染水体中的TCH具有成本低、环境友好、高效稳定、操作简单的特点,其中在吸附材料的选择上,炭基材料和矿物材料往往呈现粉末状,不易回收,对环境有二次污染的隐患,与之相比,凝胶材料适宜于对有机污染物的去除,因此,寻求一种价格低廉,吸附效果好的吸附剂是目前吸附法的研究热点.蒙脱土(MMT)作为一种土状矿物,表面带有大量永久性负电荷,晶体结构稳定,机械强度高,由于其价格低廉,易于获得,吸附性能优越的特点,在污水处理中,常用于吸附去除重金属离子、染料、酚类化合物,多环芳烃等,去除效果较好,但目前还没单独使用MMT进行TCH吸附方面的研究,鉴于此背景,旨在研究MMT吸附TCH的吸附性能和效果.通过研究,发现Freundlich等温吸附模型和准二级动力学模型对MMT吸附TCH具有较好的拟合效果,表明其吸附为多层吸附,且在60 min内即可达到总吸附量的87%,Langmuir饱和吸附量可达到118.6 mg/g.Gibbs自由能ΔG0皆为负值,表明MMT对TCH的吸附是自发过程,容易进行.计算所得焓变和熵变均大于零,说明吸附进程为吸热过程,吸附随机发生在固液表面,提高温度对吸附有促进作用,与温度影响实验所得结论一致,再次说明吸附过程为吸热反应,提高温度有利于吸附进行.溶液pH对吸附性能影响显著,pH从3增加到10,吸附量先增大后减小,最佳pH值为6~8.这是由于在强酸性条件下,H+与TCH形成竞争吸附,所以MMT对TCH的吸附量较低.当pH值提高,H+浓度降低,与TCH的竞争吸附减弱,因此MMT对TCH的静电吸附量提高.但随着pH值继续升高,TCH逐渐变为H2TC-及HTC2-形态,与带负电荷的MMT之间产生静电斥力,造成吸附量降低.根据上述实验结果和表征分析,分析机理可得,MMT对TCH的吸附过程包括同时包括物理吸附与化学作用,其中化学作用在其中占主导.MMT中的Al-O-H基团能与TCH分子上的三羰基酰胺基团以及羟基基团形成氢键作用,且在pH<5时存在一定的静电引力.综上所述,由于MMT成本低廉,对TCH的吸附速率快,吸附量大,在吸附TCH性能上有其独特优势,因此在实际含TCH废水处理中具有较好的应用前景.
Tetracycline hydrochloride(TCH)is widely used in medical,livestock breeding,and agricultural industries.However,because it is not fully absorbed by humans and animals while used,it enters environmental water bodies with feces and urine.TCH can damage the eco-logical environment,harm human health,and produce drug-resistant bacteria,posing threats to the environment and human health.There-fore,finding an economical and effective removal method is crucial for water quality safety.Currently,the removal methods for TCH in water mainly include chemical,biological,and physical methods.Compared with chemical and biological treatments,the adsorption method in physical treatments for removing TCH from polluted water bodies has the advantages of low cost,environmental friendliness,high efficiency,stability,and easy operation.In choosing adsorption materials,carbon-based and mineral materials often appear powdery,are not easily re-coverable,and carry the risk of secondary pollution.In contrast,gel materials are suitable for removing organic pollutants.Thus,finding an inexpensive adsorbent with good adsorption performance is currently a hot subject.Montmorillonite(MMT)is a clay mineral with a stable crystal structure and high mechanical strength.It has a surface with many permanent negative charges.Due to its low cost,easy availability,and superior adsorption properties,it is commonly used in wastewater treatment to adsorb heavy metal ions,dyes,phenolic compounds,polycyclic aromatic hydrocarbons,etc.,with good removal effects.However,there is currently no research specifically on using MMT for TCH adsorption.Against this background,this paper aims to study the adsorption performance and effects of MMT adsorbing TCH.Through research,it is found that the Freundlich isothermal adsorption model and the pseudo-second-order kinetic model fit well for MMT adsorbing TCH,indicating that its adsorption is multilayered and can reach 87%of the total adsorption amount within 60 minutes.The Langmuir satura-tion adsorption amount can reach 118.6mg/g.The Gibbs free energy ΔG0 is always negative,indicating that the adsorption of TCH by MMT is a spontaneous process.The calculated enthalpy and entropy changes are both positive,indicating that the adsorption process is endothermic and occurs randomly on the solid-liquid surface.Increasing the temperature promotes adsorption,which is consistent with the conclusions drawn from temperature effect experiments,further indicating that the adsorption process is an endothermic reaction and increasing the tem-perature is conducive to adsorption.The solution pH significantly affects adsorption performance.As the pH increases from 3 to 10,the ad-sorption amount first increases and then decreases,with the optimal pH range being 6-8.This is because,under strongly acidic conditions,H+ competes with TCH for adsorption,resulting in a lower adsorption amount of TCH by MMT.As the pH value increases and the H+ con-centration decreases,the competitive adsorption with TCH is reduced,so the electrostatic adsorption of TCH by MMT increases.But as the pH continues to rise,TCH gradually transforms into H2TC-and HTC2-forms,creating electrostatic repulsion with negatively charged MMT and causing a decrease in adsorption.Based on the above experiment results and characterization analysis,the mechanism suggests that the adsorption process of MMT on TCH includes both physical adsorption and chemical actions,with the latter being dominant.The Al-O-H group in MMT can form hydrogen bonds with the tricarbamoyl amide and hydroxyl groups on the TCH molecule.At pH<5,there is also a certain electrostatic attraction.In summary,due to the low cost of MMT,its fast adsorption rate,and high adsorption capacity,it has unique advantages in the adsorption performance of TCH,thus promising a bright application prospect in the actual TCH wastewater treatment.