Study On The Removal Of Ni²⁺ By Modified Algae

Heavy metal nickel is an essential element of human,but excessive nickel could cause harm to the human health.How to remove nickel from waste water was a prominent problem faced by environmental protection.Bio-adsorption as an emerging heavy metal removal method has many advantages such as wide source of raw materials,high adsorption efficiency,environmental friendliness,no secondary pollution,etc.It shows a good application prospect.The biomass of the seaweed Sargassum thunbergii,Ulva lactuca and Gracilaria lemaneiformis were treated by potassium permanganate,respectively.Biosorption of Ni²⁺onto 3 biosorbents was investigated.1.The effects of different parameters including pH,temperature,contact time,biomass dosage and initial concentration of Ni²⁺on the adsorption capacity were studied.2.The experimental data were fitted with adsorption isotherm models and kinetic models.3.The adsorption mechanism was discussed by means of scanning electron microscopy and energy dispersive spectrometry and infrared spectroscopy.The experimental results showed that the adsorption capacity of the three materials increases with the increase of pH,and tends to stabilize after pH>5.The temperature change?15-35°C?has a significant effect on the modified Sargassum thunbergii?the optimum temperature is 25-35°C?,and the effect on the adsorption capacity of modified Ulva lactuca and Gracilaria lemaneiformis were not obvious.After the modification,the equilibrium time for adsorption of Sargassum thunbergii,Ulva lactuca and Gracilaria lemaneiformis reached 120min,120min and 150min,respectively.With the increase of the amount of modified materials,the adsorption capacity of Ni²⁺decreases,and the removal rate increases significantly.The Langmuir and Freundlich adsorption isotherm model and the pseudo-first-order and pseudo-second-order kinetic models were used to fit the experimental data before and after modification.The results showed that the adsorption of Ni²⁺on the six materials conformed to the Langmuir model,and the maximum adsorption capacities of the modified Sargassum thunbergii,Ulva lactuca and Gracilaria lemaneiformis were 49.39,40.08,and 33.16 mg/g,respectively,which was 19.69%,26.75%and 28.47%higher than before modification.The results showed that the modified Sargassum thunbergii>Sargassum thunbergii>Modified Ulva lactuca>Modified Gracilaria lemaneiformis>Ulva lactuca>Gracilaria lemaneiformis.The biosorption kinetic data were successfully described with pseudo-second-order model for 3 biosorbents,indicating that the adsorption of Ni²⁺by the three materials was related to the functional groups on the surface of the material.The adsorption mechanism was discussed by means of Scanning Electron Microscopy and Energy Dispersive Spectrometry?EDS?and infrared spectroscopy.Scanning electron microscopy showed that the surface structure of the material changed significantly before and after the modification.The surface of the modified adsorbent material has increased Mn element compared with the unmodified adsorbent material.The EDS analysis showed that the Ni element was increased after adsorption,and the contents of elements such as Mg and Ca were decreased,indicating that the ion exchange reaction occurred on the Ni²⁺adsorbed by the modified material.FTIR analysis showed that hydroxyl,amino,and carboxyl functional groups may participate in the adsorption of Ni²⁺.The above results indicate that the use of potassium permanganate as a modifier to pretreat the marine macroalgae Sargassum thunbergii,Ulva lactuca and Gracilaria lemaneiformis can significantly improve the adsorption performance of the material,and can be used as an attempt to treat nickel-containing wastewater.