Abstract
The influences of mechanical milling on Indonesian Natural Bentonite (INB) characteristics and manganese (Mn) removal from acid mine drainage (AMD) were investigated. The INB characteristics were observed by scanning electron microscope (SEM), X-ray diffraction (XRD), nitrogen adsorption-desorption for specific surface area (SSA) and microporosity measurement, cation exchange capacity (CEC) and particle size distribution (PSD) analyzer. Four minutes milling with frequency 20 Hz on INB caused morphological change which showed more crumbled and destructed particle, lost the (001) peak but still retained the (100) peak that indicated delamination of montmorillonite mineral without breaking the tetrahedral-octahedral-tetrahedral (T-O-T) structure, rose the CEC from 28.49 meq/100g to 35.51 meq/100g, increase in the SSA from 60.63 m2/g to 104.88 m2/g, significant increase in microporosity which described in the t plots and decrease in the mean particle size distribution peak from 49.28 μm to 38.84 μm. The effect of contact time and effect of adsorbent dosage on Mn sorption was studied. Both unmilled and milled samples reached equilibrium at 24 hours and the pH rose from 4 to 7 in first 30 minutes. The Mn removal percentage increased significantly after milling. Using Langmuir isotherm, the maximum adsorbed metals (qmax) also increased from 0.570 to 4.219 mg/g.
Highlights
Bentonite, clay material containing montmorillonite minerals including to the smectite group, naturally formed by volcanic ash alteration or hydrothermal alteration, is widely used for environmental purposes such as adsorbent, radioactive barrier, liner disposal and so on due to its absorbability and low permeability [1,2]
Particle size distribution measurements were made by SALD-2300 laser diffraction particle size analyzer
According to the significant increase in microporosity from the t plot, but there was no significant change of t plot, it is assumed the delamination did not fully separated between the tetrahedral-octahedral- tetrahedral (T-O-T) planes
Summary
Clay material containing montmorillonite minerals including to the smectite group, naturally formed by volcanic ash alteration or hydrothermal alteration, is widely used for environmental purposes such as adsorbent, radioactive barrier, liner disposal and so on due to its absorbability and low permeability [1,2]. Some modifications have been developed to improve bentonite sorption performance such as acid activation, pillaring, and milling [3,4,5]. Milling itself is non-chemical modification technique, usually using spinning jar with stainless still balls inside. The spinning jar causes pounding motion of the balls to the sample. This ball milling process reduces the bentonite particle size, change the morphology and crystal structure, exfoliation, increase at specific surface area (SSA) and cation exchange capacity (CEC), and improve heavy metal sorption performance [6,7]. Continuous milling will gradually affect montmorillonite crystal structural change which leads to amorphization. Intensive milling process gradually increased the SSA and CEC and reached the peak which decreased [8]
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