Flocculation of chemicals known as flocculants in
Flocculation is a process ofbringing together smaller particles to form larger particles, and settling ofcolloidal particles from stable suspensions caused by the addition of chemicalsknown as flocculants in minute quantities Bratby , George .There are two types of flocculants polymers depend on theirsources, Synthetic organic flocculants: these are based on various monomerslike acrylamide, acrylic acid, diallyldimethyl ammonium chloride (DADMAC),styrene sulphonic acid etc. Natural organic flocculants: these are based onnatural polymers like starch, cellulose, natural gums and mucilages and theirderivatives Sharma et al 2006.Among the polymeric flocculants, the synthetic polymers can be tailor-made bycontrolling the molecular weight, molecular weight distribution, chemicalstructure of polymers, and nature and ratio of functional groups on thepolymeric backbone. Due to versatile tailorability, synthetic polymers are veryefficient flocculants. However, they are not biodegradable and shear-resistant.Natural polymers, mainly polysaccharides, are moderately efficient, areshear-stable, biodegradable, and inexpensive Singh et al 2000.
Water-soluble polysaccharides have myriad industrial and agriculturalapplications. It can be successfully used as flocculants Bolto.BA 1995 , Polysaccharideshave various characteristics. They are biodegradable, shear-stable,inexpensive, and easily available from renewable farm and forest resources.Depending on the source, these poly-saccharides may have manylow-molecular-weight impurities.
The biodegradability of polysaccharides reducestheir shelf life and needs to be suitably controlled. In various applications,their required dosages are large and their solutions and flocs lose stabilityand strength because of biodegradability. However, it could be modifying bygrafting synthetic monomer Nayak& Singh 2001 and cationization Singh et al 2009.Many earlier researches have been made to combine the bestproperties of both by grafting synthetic polymers onto the backbone of naturalpolymers after purification Deshmukhet al 1991 , Ungeheuer etal 1989. The advantages gainedfrom the earlier studies were the consequent reducing of biodegradability andhigh shear-stability Morgan &McCormick 1990, Singh 1995.
Bigand et al extensively study the cationization of xylan orglactomannan ( guar ) by using 2,3-epoxy propyl trimethtyl ammonium chloride asetherifying agent under alkaline condition. Reaction condition were optimizedto obtain a derivative with maximum DS value, they success to obtain 1.3 DSvalue and 48% grafting rate.Pang et al 2013 synthesize a novel organic polymeric flocculant bygrafting cationic etherifiying monomer 3-choloro-2-hydroxy-propyl trimethylammonium chloride (CHAPTAC) onto the backbone of concorb powder. The syntheticreaction was initiated by hydroxyl radical made from Fenton reagent (H2O2- FeSO4).The synthesized cationic polymer shows superiority as a novel flocculant.
Lu et al 2004 develop initiation system by adding persulfate tocerium ion, This results successful synthesis of a graft co polymer of starchwith acryl amide (AM) and diallyl dimethyl ammonium chloride (DAMAC) when thecationic degree was 22%.Mclean et al 2011 synthesize guar gum- graft poly ( AM-co-DAMAC )by using Lu et al 2004 method , The percentage of grafting was 85% and thegrafting efficiency was 79.16%.Rezali et al 2012 study the process optimization of grafting DAMACmonomer onto cassava starch backbone using cerium nitrate free radicalinitiator without persulfate and they got 14% cationic degree.
Singh et al 2004 work in developing microwave assisted synthesis ofguar- g-poly acrylamide, Their work results very short reaction time and highgrafting efficiency 66.66% in just 0.22 min.Acacia gum (Arabian gum)Acacia gum is a natural arabinogalactan-protein type polysaccharidewidely used in industrial applications. The two varieties of Acacia gum, acaciasenegal and acacia seyal, are hyperbranched polysaccharides rich in arabinoseand galactose .
senegal presented the highest degree of branching 78.2 % compared to 59.2 % for seyal Lopez-Torrezet al 2015.The weight average molecular weight of acacia seyal is atleast three times greater than acacia senegl, The average molecular weight ofacacia seyal species is between 1.7 * 106to 2.1 *106 compared to 0.6*106 for acacia SenegalHassan et al 2005.