Experimental Study On Arsenic Removal From Water By Volcanic Rocks

Volcanic rocks widely exist in nature.At present,volcanic rocks are mainly used in environmental protection building materials and water treatment filter materials.In this paper,volcanic rocks are used as adsorbents to remediate arsenic pollution in water.The advantages and disadvantages of seven modification methods are compared.Sulfuric acid-calcination method is used to modify volcanic rocks jointly.The effects of solution pH,dosage,temperature and coexisting ions on arsenic removal in volcanic rocks are investigated.Isothermal adsorption line and adsorption kinetics are studied.The regeneration effect of modified volcanic rocks is improved.Finally,the volcanic rocks before and after modification were characterized by X-ray fluorescence?XRF?,scanning electron microscopy?SEM?,specific surface area test?BET?,X-ray diffraction?XRD?and Fourier transform infrared spectroscopy?FTIR?.The main conclusions are as follows:?1?The arsenic removal ability of the volcanic rocks modified by hydrochloric acid,sodium hydroxide and polypropylene decreased,while the adsorption capacity of CTAC-modified volcanic rocks to arsenic?III?increased,and the arsenic removal efficiency of the volcanic rocks modified by sulfuric acid,ferric chloride and ferrous sulfate increased significantly.The results show that sulfuric acid-calcination combined modification is the final modification method.The sulfuric acid concentration should be 1.0 mol/L in the modification process,the calcination temperature should be 300 C,and the removal efficiency of arsenic?III?and arsenic?V?by sulfuric acid-calcination combined modification of volcanic rocks can reach more than 90%.Compared with natural volcanic rocks,the removal rate of arsenic can be increased by 20%.?2?The arsenic removal efficiency of natural volcanic rocks is not high.The arsenic removal efficiency of the volcanic rocks modified by sulfuric acid-calcination increases greatly,and the adsorption effect is best at pH 6.The removal rate increases with the increase of solution temperature and volcanic rock dosage.Ions consuming OH^-in water can promote the arsenic removal process of volcanic rocks.PO₄^3-has obvious inhibition effect on the adsorption process,which is calculated by Langmuir isothermal equation.The maximum adsorption capacity of arsenic?III?and arsenic?V?by modified volcanic rocks is 5968.01?g/g and 6395.50?g/g,respectively,which is about 50 times higher than that of unmodified volcanic rocks.The adsorption process is more consistent with Lagergren quasi-second-order kinetic model.?3?Comparing the effects of nine regeneration methods,sodium carbonate and ultrapure water have little effect on the regeneration of modified volcanic rocks,all of which are below 10%.Sodium hydroxide,hydrochloric acid,EDTA,acetic acid and ultrasound can play a certain role in regeneration,and sulfuric acid has the best effect on the regeneration of modified volcanic rocks.When the solid-liquid ratio is1:10,it is determined that 0.5 mol/L¹.0 mol/L sulfuric acid is most suitable for the regeneration of modified volcanic rocks.After regeneration,the adsorption of arsenic?III?and arsenic?V?can reach more than 90%of the original.The regeneration effect of modified volcanic rocks increases with the increase of time.At 60 minutes,the regeneration effect is basically the best,and the regeneration effect is above 90%.After 5 times of regeneration,the regeneration effect decreases obviously,and the reuse times of modified volcanic rocks should be controlled within 5 times.?4?Characterization analysis of the volcanic rocks before and after modification shows that Mg,Al,Ca,Fe,Mn and other metal ions in the volcanic rocks can co-precipitate with arsenic anions to promote the removal of arsenic in water.The surface of the modified volcanic rocks is grooved,microporous,with a large number of flocculent structures,and the specific surface area increases,which is consistent with the results of specific surface area measurement.The crystal structure of natural volcanic rocks and modified volcanic rocks are mainly composed of feldspar minerals.Aluminum silicate crystal structure appears after modification.After modification,the types of functional groups of volcanic rocks do not change much,but the hydroxyl groups adsorbed by arsenic increase greatly.