Evaluation of flocculation characteristics of kaolinite dispersion system using guar gum: A green flocculant

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۴٫۲۷۶ در سال ۲۰۲۰

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۲۶ در سال ۲۰۲۱

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۰٫۹۰۱ در سال ۲۰۲۰

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Q1 در سال ۲۰۲۰

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Evaluation of flocculation characteristics of kaolinite dispersion system using guar gum: A green flocculant

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Evaluation of flocculation characteristics of kaolinite dispersion system using guar gum: A green flocculant


This  paper reports the systematic investigation on  the flocculation, sedimentation and consolidation characteristics of kaolinite using guar gum as a green flocculant. In-situ flocculation behavior of kaolinite at various pH, guar gum dosages, and ionic strength were studied using a light scattering technique. The effect of  these parameters on  the settling rate, solid consolidation, and supernatant liquid clarity was recorded.  The   morphology  of   kaolinite  and  flocculated kaolinite  aggregates  were  analyzed  using FESEM. The  morphology studies suggest that it is poorly crystalline with multiple steps on  edge, broken edge; laminar with high aspect ratio and have rough basal surface. The  complex irregularity on  the basal surface and the presence of multiple steps in the edges, broken edges (hydroxyl groups) have facilitated the guar gum adsorption. The  isoelectric point of kaolinite is pH 3.96. The  pH, ionic strength and floccu- lant dosage have a significant effect on  the kaolinite settling rate. The  guar gum has exhibited excellent turbidity removal efficiency at pH 5. The turbidity removal is inefficient at pH 10. However, guar gum has shown high turbidity removal with 80% transmission at pH  ۱۰  in  the presence of a KNO3  electrolyte.

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  1. Introduction

The  removal of  water from mineral tailings by  flocculation is one  of the major mineral processing activities. Recently, synthetic flocculants like  polyacrylamide are  in use  for the sedimentation of minerals from the process tailings and wastewater. However, their environmental  compatibility is  a  matter of  great  concern. Pre- sently, the demand for green flocculants is increasing due to  their environmental compatibility.

Guar  gum is  also  known as  guaran. It  is  a  natural non-ionic polysaccharide composed of galactose and mannose. It is a chain of      (۱ ? ۴)-linked    b-D-mannopyranose    units    with    a-D- galactopyranose  units   connected  to    the   mannose  backbone through (1 ? 6) glycosidic linkages. The  poly-mannose chain ran- domly substituted with galactose units at mannose-to-galactose ratio  of  ۱٫۸–۱٫۰  [۱,۲].   The   molecular  weight  of  guar  gum  is

۱     ۱۰۵ to  ۲۰     ۱۰۵ [۱,۲].

Ma and Pawlik [3] studied the adsorption behavior of guar gum on  kaolinite and other oxide minerals at different pH, background electrolyte, and ionic   strength. One  of  the  major conclusions of their study is  that the adsorption density of  this polysaccharide

does not  depend on the pH. However, there is a significant increase in adsorption density on kaolinite surface in the presence of chao- tropic K+  ion.  The  hydrogen bonding is the primary mechanism of guar  gum  adsorption  onto  the  kaolinite surface. The   polymer adsorbed onto the mineral surface through hydrophobic interac- tion, hydrogen bonding, chemical and  electrostatic  interaction [4–۸]. Wang et  al.  [۹]  concluded that  the hydrogen bonding is the principal force  for the adsorption of guar gum onto the talc  sur- face.  Mhlanga et al. [10]  also  reported the guar gum adsorption on several pure minerals such as talc,  pyroxene, plagioclase, chromite, and chalcopyrite. The above studies show that guar gum has  a nat- ural affinity towards these mineral surfaces. The majority of these works were carried out  to  understand its  application as a depres- sant in  flotation and selective flocculation system. However, not many reports are  available regarding its  possible use  as  a floccu- lant. The   effect  of  guar gum as  flocculant  on   the  flocculation characteristics of kaolinite particle regarding floc growth, colloidal stability and,  solid consolidation are  not  well  understood. More- over,  the flocculation characteristic method is poorly studied.

Guar  gum has  many applications in  mining and mineral pro- cessing industries. Many researchers have reported its use  in froth flotation and flocculation process [9,11]. In the froth flotation pro- cess, guar gum is used as a depressant for talceous gangue minerals for the flotation of base metals and platinum group metals bearing

ores   [۹,۱۱]. Guar   gum adsorbs onto the talc   surface to  make it hydrophilic.  It   also    has    application  as   a   binder  for   water- insoluble slimes in  the potash flotation process [12].  Guar   gum and grafted derivatives of guar gum have been explored as floccu- lants for  dewatering applications [13–۱۵]. Nasim et al.  [۱۳]  have reported a high settling rate of kaolinite using guar gum and poly- vinyl  alcohol grafted guar gum as flocculants. Apart from guar gum other polysaccharides and their grafted derivative such as chitosan [16,17], starch [18],  xanthan gum [19]  and tamarind kernel [20] have also  been explored as flocculants.

The  Indian iron ore  contains a  significant amount of  gangue minerals such as silicates and aluminium silicates. These minerals liberate at finer sizes. Therefore, the tailings generated in  an  iron ore  processing plant are  fine  in size.  One of our  earlier studies sug- gests that d80 of the tailings is 12 mm. The tailings contain 5%-10% solid (w/w) and the Al2O3, SiO2  content in the tailings are  ۱۸% and

۱۴%, respectively [4]. The fine  particle causes a serious problem in the dewatering process. Thus,  the consolidated solid in  the thick- ener contains high moisture, which in  turn creates technical and economic difficulties in handling, disposal, and water removal.

The  basal faces  of 1:1  tetra-octahedral aluminosilicate consists of tetrahedral siloxane (-Si-O-Si-) species and octahedral, alumina (Al2O3) sheet [21].  Van  Olphen [21]  showed that the basal faces having a  siloxane structure  carry a  permanent  negative charge due to  the isomorphous substitution of Si4+  by  Al3+  groups.  Also, aluminum (Al-OH)  and silanol (Si-OH)  groups occur at the edges. Therefore, the edge faces  are  charged by protonation and deproto- nation of hydroxyl groups depending on the pH [21,22]. These par- ticles are  highly charged at neutral and alkaline pH  and shows stable dispersion behavior. Therefore, authors choose kaolinite an aluminium silicate to  study its  flocculation characteristics in  the presence of guar gum.

The design of a dewatering system requires a thorough analysis of the solid-liquid system and slimes stability behavior. The stabil- ity of particle can  be changed by controlling the pH, ionic  strength, addition of flocculant and coagulant [4,23–۲۸]. In flocculation, the fine  particles interact with the flocculating agent and aggregate to form flocs.  The  flocs  settle rapidly under the influence of gravity. The  characteristics of floc decide the rate of settling and moisture contents  of  consolidated  tailings  [۲۹].   The   floc   characteristics depend on  several factors such as  particle surface chemistry, size distribution,  density, shape;  viscosity and dielectric constant  of suspension; chemical nature, molecular weight, charge and charge density of the flocculants [30,31].

The environmental policies have enforced legal  rules for the dis- posal of waste by the mineral industries. It is essential to redesign the dewatering operation to meet the current challenges. The pre- sent work has been undertaken to study the sedimentation behavior of kaolinite using guar gum as a flocculant. The spectroscopic tech- niques are  used to  understand the influence of  different process parameter on the flocculation and consolidation characteristics.

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