This work describes the features of cellulose acetate/hydroxyapatite composite membranes. The capacity of cellulose acetate/hydroxyapatite composite membranes for remotion of lead ions from aqueous solution was investigated. Cellulose acetate/hydroxyapatite composite membrane has shown an ability to retain Pb2+ ions from aqueous solutions. Cellulose acetate/hydroxyapatite composite membrane was effectual in taking Pb2+ ions from solutions with 81 % Pb removed. The effectual remotion of Pb2+ ions from aqueous solution suggests that porous cellulose acetate/hydroxyapatite composite membranes have the possible to immobilise Pb2+ ions in lead-contaminated effluents.
Keywords: cellulose ethanoate, hydroxyapatite, composite, lead ions removal
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Lead can be toxic for worlds and animate beings at some concentrations and it is a serious public wellness issue worldwide. Extensive studies and reappraisals are available on the immunological, neurological and carcinogenic effects of ague to chronic lead exposure by the inspiration, unwritten and cuticular paths of disposal. Consequently, extended attempt has been made to handle Pb-containing wastes. Assorted methods have been proposed for the remotion of lead from effluents. Chemical precipitation, solvent extraction, electrochemical technique, ion exchange, biosorption, and surface assimilation are several of the often used procedures [ 1-3 ] .
Hydroxyapatite [ Ca10 ( PO4 ) 6 ( OH ) 2 ] is the most of import bioceramics stuffs for its alone bioactivity and stableness. Besides, hydroxyapatite is a good inorganic ions fixators and it can acknowledge a series of cationic and anionic permutations in its construction. Several surveies have recognized the capacity of hydroxyapatite to adhere bivalent heavy metal ions ( Pb, Cd, Zn, Sb and V ) from aqueous solutions [ 4-6 ] . At the same clip, ion exchange reaction between Ca2+ ions that exists in the hydroxyapatite construction and positive ions in the solution is possible. Therefore, it shows superior remotion rate for divalent positive metal ion through ion exchange between heavy metal bing in H2O and Ca2+ ion of hydroxyapatite.
Cellulose ethanoate is one of the most of import man-made organic esters because of its wide applications, such as in fibres, movies, and membranes, and because it is made from cellulose, the most abundant biopolymer on Earth. In recent old ages, natural cellulose stuffs have gained attending as stages for polymer complexs [ 7-10 ] .
In this survey, the hydroxyapatite was deposited on cellulose acetate surface to use its ion-exchangeability. The capacity of cellulose acetate/hydroxyapatite composite membranes for remotion of lead ions from aqueous solution was investigated.
The cellulose ethanoate membranes were prepared by stage – inversion method utilizing cellulose acetate polymer, propanone as dissolver, formamide or H2O as non-solvents, whereas H2O was used as curdling medium. A simple Supersaturated Calcification Solution ( SCS ) with high Ca and phosphate ion concentrations was used for biomimetic coating survey. The morphology and belongingss of the hydroxyapatite/cellulose ethanoate composite movies were characterized by field emanation scanning negatron microscopy ( Fe-SEM, with Fe-SEM MIRA II LMU CS 01 TESCAN microscope ) and pore sizes measuring. Further inside informations on the stuffs processing and several belongingss of membranes and complexs used in this survey can be found elsewhere [ 11,12 ] .
The remotion of Pb2+ ions was studied on pure cellulose ethanoate membranes and hydroxyapatite/cellulose acetate composite membranes. Kinetic reaction of Pb remotion by membranes was examined by a batch experiment. A sample of each membrane was immersed to 100 milliliter of solution incorporating a Pb concentration of 1000 mg/l prepared by Pb ( NO3 ) 2. The solution was stirred for a certain period of clip at room temperature ( 25 0C ) . During experiments, solutions samples were taken and the lead concentration of the solution was determined by photocolorimetric method with dithizone, utilizing a FEK-M photocolorimeter.
Consequences and treatment
Cellulose acetate porous membranes prepared in our laboratory consist of 3-dimensional polymeric construction, with pore sizes of molecular dimensions [ 11 ] .
Biomimetic intervention in SCS used in our survey consisted in formation and deposition of hydroxyapatite bed on the active surface of cellulose acetate membranes. The hydroxyapatite formed on cellulose acetate membranes soaked in SCS was examined by field emanation scanning negatron microscopy ( Fe-SEM ) . In SEM image of the cross-section of cellulose acetate membrane immersed in SCS, the hydroxyapatite sedimentations were observed ( Fig. 1 ) .
Fig. 1. SEM image of the membrane sample after soaking in SCS for 120 H
In this survey, the capacity of cellulose acetate/hydroxyapatite composite membranes for remotion of lead ions from aqueous solution was investigated. Removal of Pb2+ ions was performed utilizing 1 – 2 g of membrane sample and the clip for intervention varied runing from 1 to 3 H.
First, we studied the influence of pH on the procedure of keeping of lead from aqueous solution. Under the experimental conditions, the fluctuation of lead remotion per centum with solution pH is shown in Fig. 2a. It can be observed that removal per centum decreases as solution pH increasing. The best remotion per centum occurs under acerb status ( pH=3 ) ; it is about 81 % .
Fig. 2. Lead remotion by cellulose acetate/hydroxyapatite composite membrane. The influence of: pH ( a ) and contact clip ( B )
Besides, the influence of contact clip on lead remotion is investigated. As shown on the Fig. 2b, a rapid kinetic reaction of Pb remotion occurred within the first 10 – 30 min, at pH=3. The aqueous Pb concentration at 30 min decreased from 1000 mg/l to 965 mg/l by pure cellulose ethanoate membrane and from 1000 mg/l to 229 mg/l by cellulose acetate/hydroxyapatite composite membrane. In contrast to the pure cellulose ethanoate membrane, cellulose acetate/hydroxyapatite composite membrane had a superior rate of aqueous Pb remotion and removed 81 % aqueous Pb within 100 min. The consequence on the rapid kinetic reaction of Pb and hydroxyapatite agreed with those described elsewhere [ 14,15 ] .
The crystallinity of the hydroxyapatite stage is expected to impact the mode by which heavy metal ions are removed from solution stage. Highly crystalline stages, such as hydroxyapatite, have a comparatively low solubility. A low solubility hydroxyapatite stage may prefer surface-mediated metals removal mechanisms, e.g. , sorption or ion-exchange, or possibly heterogenous nucleation and precipitation at the crystal surface. Mechanisms for Pb ions keeping by hydroxyapatite is the surface assimilation of Pb2+ ions on the hydroxyapatite surfaces followed by the ion-exchange reaction between Pb2+ ions adsorbed and Ca2+ ions of hydroxyapatite [ 4,13,14 ] .
These consequences showed that the cellulose acetate/hydroxyapatite composite membrane can be used as an effectual adsorbent for taking Pb ions from aqueous solution.
The asymmetric porous cellulose ethanoate membranes were fabricated by wet stage inversion method. The SEM images of the cellulose ethanoate membranes grounds the dissymmetry / heterogeneousness of these systems. The Supersaturated Calcification Solution ( SCS ) was used to look into hydroxyapatite formation on cellulose acetate matrix. Besides, the capacity of cellulose acetate/hydroxyapatite composite membranes for remotion of lead ions from aqueous solution was investigated. Cellulose acetate/hydroxyapatite composite membrane has shown a certain ability to retain Pb2+ ions from aqueous solutions. These composite membranes were effectual in taking Pb2+ ions from solutions with 81 % Pb removed. The remotion of Pb2+ ions from aqueous solution suggests that porous cellulose acetate/hydroxyapatite composite membranes have the possible to immobilise Pb2+ ions in lead-contaminated wastes.