Research On Phosphate Adsorption Behavior From Aqueous Solution Using Three Kinds Of Porous Clay Composite Materials

Eutrophication is a serious water pollution concerns on a global scale, resultingfrom excess phosphate in water. Therefore, controlling the phosphate concentration issignificant to deal with eutrophication. Adsorption is popular among different kinds ofmethods, since it is less space demand, easy to operate, more economical, effectiveand environment friendly.Most adsorbents are natural or synthetic materials, such as natural soil materials,zeolite, blast furnace slag, fly ash and so on. Some of them can only be used in anarrow pH rang, some of them are too expensive, and most of them are powders,which would make pipe to be blocking and be difficult to recover. This researchfocused on making three kind of clay composite materials based on loess,montmorillonite and dolomite, loading La（NO₃）₃·6H₂O, Ca2+（from shell） andAl₂（SO₄）₃, respectively. It also focused on phosphate removal adsorption behaviorfrom aqueous solution using three kinds of clay composite materials.This research investigated phosphate removal efficiency was effected by dosage,reaction time and pH. Loaded La（III） porous clay material can be efficient to removephosphate when pH was between4.00to11.00（phosphate removal efficiency wasabove95.2%）. Loaded Ca（II） porous clay material can be efficient to removephosphate when pH was between2.30to12.01（phosphate removal efficiency wasabove97.8%）. Loaded Al（III） porous clay material can be efficient to removephosphate when pH was between2.99to6.94, it was also efficient when pH wasbetween8.97to12.01（phosphate removal efficiency was above98.5%）. All of themcan be used in a wide pH range. The adsorption process fitted to thepseudo-second-order kinetic model rather than pseudo-first-order, it also fitted tointra-particle diffusion model, illustrating this process included external surfaceadsorption （macro-pre diffusion） and internal surface adsorption （micro-porediffusion）. Langmuir model gave more satisfactory fitting to the adsorption isothermon clay composite materials than Freundlich model, suggesting it had monolayeradsorption on adsorbent surface. The adsorption was not only chemical process, but also included physical process. The thermodynamic parameters were calculated byGibbs equation, indicating adsorption was spontaneous and endothermic, randomnessincreased at the solid-liquid interface during the phosphate adsorption process. Themain adsorption force of loaded La（III） porous clay material and loaded Ca（II） porousclay material was hydrogen bonding force and coupling reaction force. The mainadsorption force of loaded Al（III） porous clay material was chemical bonding forceand ligand exchange force.Furthermore, the characterization of these clay materials were tested, suggestingall of them were effective adsorbent for phosphate removal from aqueous solution dueto their hierarchical porous structures （phosphate removal efficiency were above95%）.According to the SEM and EDS of original adsorbents and treated adsorbents, theadsorption process of La（III） porous clay material and loaded Ca（II） porous claymaterial included chemical precipitation and electrostatic attraction. The adsorptionprocess of Al（III） porous clay material included ligand exchange, chemicalprecipitation and electrostatic attraction.