Study On Adsorption Capability Of Humic Acid-coated Hydroxyapatite Removal Of Heavy Metal Ion

In recent years,water pollution has been attracted more attention.Treatment methods of heavy metal wastewater are varied,and the adsorption is widely used due to its low cost,less secondary pollution as well as other advantages.In this paper,a humic acid-coated hydroxyapatite?HA/HAP?was synthesized and characterized.The heavy metal ions(Cu²⁺,Pb²⁺,Cd²⁺and Zn²⁺)in aqueous solution were used as target pollutants.The adsorption process and adsorption behavior of heavy metals on HA/HAP were studied.The adsorption mechanism was analyzed using the simulation method of Materials Studio.Humic acid-coated hydroxyapatite composite adsorbent were characterized by scanning electron microscope,X-ray diffraction,BET and Fourier Transform Infrared.The results showed that The HA/HAP particle size ranged from 1?m to 90?m.The specific surface areas of HA/HAP and hydroxyapatite were 57.02m²/g and 60.38m²/g,respectively.The average pore volume was 0.54cm²/g and 0.3cm²/g,respectively.The average pore size is 37.61nm and19.85nm,respectively.Hydroxyapatite successfully was modified by humic acid and crystal structure of hydroxyapatite has not changed.The results showed that the adsorption rate of heavy metal by HA/HAP increased with the increase of dosage of adsorbent,pH,contact time and temperature.The optimal adsorbents for HA/HAP adsorption of Cu²⁺,Pb²⁺,Cd²⁺,and Zn²⁺were 0.8g,0.2g,0.8g,and 1g,the optimal pH values were 6,7,6,and 6,and the best contact time was 45min-180min,respectively.In addition,the adsorption of heavy metal ions by HA/HAP was influenced by interference ions(K⁺,Ca²⁺,Na⁺),of which Ca²⁺had the most interference.The results of thermodynamics showed that the adsorption process of heavy metals by HA/HAP is spontaneous,endothermic and sustainable.The adsorption of Pb²⁺,Cd²⁺and Zn²⁺are well described by the Langmuir adsorption isotherm model,and the adsorption of Cu²⁺conforms to the Freundlich adsorption isotherm model.The kinetic results showed that the adsorption rate was controlled by the chemisorption process.Adsorption mechanism of the study showed that which was mainly described as a complexation reaction between carboxyl and hydroxyl groups of HA/HAP and heavy metal ions,as well as the electrostatic attraction between them.