Preparation Of Silica Composite Xerogels And The Application In The Treatment Of Nickel-containing Wastewater

Silica gel is a porous material with three-dimensional network structure and large pore volume and specific surface area.It has a wide range of applications in the fields of biology,medicine,chemistry,catalysis and so on.The synthesis of silica gel is mainly based on tetraethyl orthosilicate?TEOS?the hydrolysis and condensation as a silicon source under acidic or alkaline catalysis.Surfactants can also be added to the reaction media to adjust the pore characteristics of SiO₂ material.Since the aqueous solution of the organic amine surfactant is strongly alkaline,the organic amine can be used as both a porogen and a catalyst during the synthesis of silica gel.Thus,organic amine molecules and related amino groups will be present in the synthesized silica gel.The combination of nickel ions and hydroxide will form nickel hydroxide precipitating from the nickel-containing.Based on this,the amine-containing silica gel can be used to remove and recover nickel ions in wastewater.In the experiments,butylamine?BA?,octylamine?OA?and dodecylamine?DA?were added to synthesize silica gel.Scanning electron microscop,transmission electron microscop,X-ray diffraction analysis,energy dispersion spectrum analysis,X-Ray photoelectron spectroscopy,infrared spectroscopy,N₂ isothermal adsorption,thermal analysis,nuclear magnetic resonance spectroscopy,organic element analysis,etc.were used to characterize the gel,and the role of organic amines in the synthesis of silica gel was analyzed and discussed.The feasibility of removing nickel ions from simulated and actual wastewater by sillica gel was studied,and the treatment of recovered sediment and secondary waste liquid was studied.XPS results confirmed that there are both protonated and non-protonated amino groups in the gel synthesized by the three organic amines.As the alkyl chain grows,the ratio of the former to the latter gradually decreases.The amino groups were assembled with silica species into SiO₂ composite gels through electrostatic attraction and hydrogen bonding,respectively.Si²⁹ nuclear magnetic resonance spectroscopy showed that Q⁴ units were the most in butylamine-synthesized gels,while octylamine and dodectylamine-synthesized gels contained only Q³ and Q² units but with lower content of Q⁴ units.As the carbon chain of the organic amine grows,the diameter of the microspheres that make up the gel gradually increases.The silica gels synthesized by butylamine and octylamine were in the form of blocks after drying.They are macroporous materials with high specific surface area before calcination.In contrast,all the gel synthesized by dodecylamine was in the form of powder.There was little porosity in this sample before calcination,and its surface area was very small.The microporous gel with high specific surface area was obtained after the dodecylamine was removed.The content of amine in the gel increased with the length of the alkyl chain,which accounted for 11.81wt%,31.11wt%,and 46.07wt%in the three gels,respectively.The SiO₂ composite gel containing organic amine was strongly alkaline in water,and the gel synthesized by adding BA showed the strongest alkaline feature.This gel was added into synthesized nickel wastewater,and nickel ions formed a precipitate which was confirmed as Ni?OH?₂.In the whole process of removing nickel ions in water,the gel continuously released amine molecules into solution to supply hydroxide groups to maintain a stable pH environment for the precipitation.In addition,the added xerogel was solid blocks and could be easily recovered and reused.Experiments have shown that the efficiency of nickel removal remained unchanged when silica gel was reused three times.The recovered precipitates are microspheres consisting of aggregated nanosheets,which contained trace amount of dissolved silica gel.The collected precipitate and the recycled gel could be used as a glass colorant.After an industrial nickel wastewater was pretreated with CaO,the silica gel was used to remove the left nickel ions.And the solution obtained after the treatment of synthetic and industrial nickel wastewaters was reused in the synthesis of silica gel.