Removal of some heavy metals from wastewater by using diatomaceous earth

Abstract

The aim of this work is stydying the removal of some divalent cations, Cd, Cu, and Co from their aqueous solutions by using the natural materials, diatomite. The diatomite material was characterized by the chemical analysis, IR, X-ray and TEM also the surface area was calculated. The results of characterization indicate that diatomite consist mainly from silica with some other oxide. The effect of pH values and the initial concentrations of the aquous solution on the efficiency of removing was studied. The results indicate that the efficienc of removing dependsgreatly on the pH values and the initial concentration of the cations with optimum value for each case. In general the effeciency of removing for these cations follows the following sequence Cd>Cu>Co. This behavior may due to the electronegativity and the ionic radius as well as the different species of these cations in their solutions.

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ISSN: 0975-8585
May-June 2014 RJPBCS 5(3) Page No. 198
Research Journal of Pharmaceutical, Biological and Chemical
Sciences
Removal of Some Heavy Metals from Wastewater by Using Diatomaceous Earth.
Adly A Hanna, Marwa A Sherief*, and Reham MM Aboelenin.
National Research Centre, Dokki, P.O.Box: 12622, Postal code: 11787, Cairo, Egypt.
ABSTRACT
The aim of this work is stydying the removal of some divalent cations, Cd, Cu, and Co from their aqueous
solutions by using the natural materials, diatomite. The diatomite material was characterized by the chemical
analysis, IR, X-ray and TEM also the surface area was calculated. The results of characterization indicate that
diatomite consist mainly from silica with some other oxide.The effect of pH values and the initial concentrations of
the aquous solution on the efficiency of removing was studied. The results indicate that the efficienc of removing
dependsgreatly on the pH values and the initial concentration of the cations with optimum value for each case. In
general the effeciency of removing for these cations follows the following sequence Cd>Cu>Co. This behavior may
due to the electronegativity and the ionic radius as well as the different species of these cations in their solutions
Keywords: Diatomaceous earth- adsorption – heavy metals- characterization- concentratrions
*Corresponding author

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INTRODUCTION
Waste streams encountered in mining operations, and various chemical processing
industries, contain heavy metals which are non- biodegradable, toxic priority pollutants. Due to
their tendency to accumulate in living organisms causing various diseases and disorders, the
treatment methods for metal- bearing effluents are essential for environmental and human
health protection. Among numerous commonly used techniques for water purification,
adsorption technologies have gained the most attention because of their low cost and easy
operation [1,2]. In recent years, an intensive research was can ducted on the technologies of
adsorption. Focusing on the selection and /or production of low- cost adsorbents with good
metal- binding capacities, which could be utilized as an alternative to the most widely used
adsorbent in wastewater treatment- activated carbon. Natural materials of both organic and
inorganic nature (such as chitosan, zeolites, clay and clay materials, etc) and certain waste
products from industrial operation (such as fly ash, coal, oxides and silicates)are classified as
low- cost adsorbents because they are economical and locally available [3,4]
Diatomite (DE) is fine grand, low density biogenic sediment, which consists essentially of
diatoms. It is the fossilized remnants of diatoms, tiny plunktonic algae residing in all the earths
water[5]. The death of large numbers of diatoms in an area leads to sedimentation of the
minerals present in the cell walls leading to large depositsin their high purity, often greater than
85% silica [6]. As a result diatomite is both non-toxic and odourless, present naturally in large
quantities and at high purities and it is available at low cost. Diatomite is of particular interest
due to its unique properties such as high porosity, high permeability, small particle size, high
surface area, low thermal conductivity, and chemical intertness [7].These properties of
diatomite led to its early use for water purification, in which it was used to remove particulate
matter from water for applications[6].
In previous work, the authers used some natural metals such as calcite and dolomite to
remove some impurities[8]. On the other hand they used some prepared materials such as
hydroxyapatite for purification of waste water[9].
Cd+2is very toxic, which can couse serious damage to the kidneys and bones. It is known
for its toxicity and for its association with Itai-Itai desease[10]
Copper is one of the biologically essential ions but is only required at low concentration,
Concentrations4 higher than 1.0-1.5 mg/l in water lead to enviromental and health
problem[11].
Although necessary for good health to the cobalt as a part of vitamin B12, the high or
low levels of cobalt in the aqueous medium couse some health problems[12].
The aim of this study was to investigate the efficiency of low – cost adsorbents
(diatomite) to remove some heavy metals from wastewater. Such as (Cd+2 ,1Cu+2, Co+2,) and

ISSN: 0975-8585
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study the effect of some parameter such as (pH, initial concentrations) on the efficiency of
uptaking for each cation.
MATERIALS AND METHODS
Natural (DE) was used without purification except washing with distilled water. It was
charactezied by various techniques. Infrared absorption spectra (IR) were performed by the KBr
disc technique using a fourier transformer infrared between 400 to 4000 cm-1. X-ray
diffraction, XRD, was carried out by using Brukur D8 advance diffractomer (Germany) using
CuKα radiation. The surface area of the natural DE was performed by using Quanachrome Inst.
Quantachrome Nova Automated gas sorption system version 1.12. Transmition electron
microscope (TEM) was performed to study the morphology of DE.
The dried DE was used as adsorbent to remove some divalent cations, Cd, Cu,Co from
their aquous solutions.
In this work, 0.1 gm of the DE powder was dispersed in 20 mm3aqueous solutions
containing different concentrations of the divalent cations nitrates. The pH values of the
solution were adjusted by adding 1N HNO3 solution at 30 ºC, the solutions were left for 24h to
attain the equilibrium state. After this period the solid parts were separated by filtration, the
filtrate was analyzed by using atomic absorption route to determine the remainder amounts of
Cd, Cu, andCo. The effect of the concentration of the divalent cations between 5-30 ppm and
PH of solutions between 2-11 were investigated. The efficiency of removing was calculated by
using the following formula, %= (C0 – C)/ C0, where C0 and C are the initial and the concentration
of the divalent cations in the solution after removing respectively.
RESULT AND DISCUSSION
I-Characterion of DE sample
The chemical analysis of the DE sample shows that it consists mainly of silica (SiO2=
83.6) with relatively small percentage of other oxides such as Al2O3, Fe2O3, CaO, and other
oxides, Table 1[13]. In comparison with other diatomite’s
it is clear that the silica content is nearly similar to silica content in china(14), Turkey(15),
diatomite. From the results of the chemical analysis, it may conclude that the diatomite
behaves in a similar way to amorphous silica due to the large quantity of silica present in its
structure
Table 1: chemical analysis of diatomite earth
Oxide
SiO2
Al2O3
Fe2O3
TiO2
Na2O
K2O
CaO
MgO
Loss/others
Percentage
83.6
4.24
1.07
–––
––––
–––
6.17
–––
4.86

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IR –spectra
The IR charts of the natural sample was illustrated in (Fig 1).From the chart, a series of
absorbance bands were appeared at (790, 1000-1200 Cm-1) corresponding to the silicates
structure as pointed out [16]. Also, at 1080 cm-1, a wide absorption band was appeared due to
the vibration of the Si-O-Si. Also, a weak absorption band appeared at ~ 600 cm-1 which
corresponding to Si-O deformation and Al-O stretching.
X-ray diffraction pattern:
The X-ray charts of the samples (Fig 2) indicate that the specified peaks of the silicon
were illustrated, as reported [17].
Figure 1: IR spectra of natural diatomaceous earth, DE
Figure 2: XRD of natural diatomaceous earth, DE

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Transmission Electron Microscope (TEM):
Examining DEs samples with (TEM) (Fig 3), showed that the natural DE has very small
number of crystals with the sharp edges and its surface area as calculated from the TEM equals
to 7.3 m2/g . The shapes of crystals and the high surface area favored the using of the DE for
removing the heavy metals.
Figure 3: TEM of natural diatomaceous earth
Removing of di valent cations by DE:
In order to provide a quantitative description of Cd, Cu, Co onto diatomite surface, two types
of adsorption experiments were carried,
(i) Adsorption of constant initial metal concentration as a function of pH.
(ii) Adsorption at constant pH as a function of metal concentration in its solutions.
In this study, the batch process was performed, where a certain weight of DE(0.1gm)
was immersed in nitrate solutions of the divalent cations (Cd, Cu, Co) at the same concentration
of these cations with continuous stirring to attain the equilibrium state (t= 24h) and pH =
2,4,6,8and 10 were adjusted by using the puffer solutions.
A study on the effect of the pH values of removing the considered cation from their
aqueous solution was performed and the results were represented in Fig 4.Generally, it is
observed that the effeciency of removing for the three cations increases as the pH value
increases until reached to steady state.
2 4 6 8 10
88
90
92
94
96
98
100
effeciency (%)
pH
Cu
Co
Cd
Figure 4: effect of Ph on the effeciency of removing cations

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This state depend on the nature of the cations, where it recorded between 8-10 pH
values for Cd+2 , 4-5.5 values for Cu+2[18] ,and 6-7 values for Co+2[19,20]. From these values it
may conclude that the removing of Cd+2 is favoured at in the basic medium, while for Cu+2 at
the acidic medium and for Co+2 in nearly neutral medium, this variation may due to the
electronagitvities of there cations where it equals 1.69 for Cd+2, 1.9 for Cu and 1.9 for Co. On
other hand it depend on the ionic radius which equal 0.97for Cd, 0.73 for Cu, and o.74 for Co.
Due to the difference in both the electronegativity and ionic radius of the considered cations,
the removing of the three cations behave the following sequence Cd < Co <or=Cu where:-
(i) The more electronegative ions will be more strongly attracted to the surface of the
diatomite
(ii) The smaller ionic radius will be easily enter into the smaller pores and have greater
access.
Also, it is observed that the efficiency of removing Cd+2 increases smoothly from pH =2
to pH =8, and the effeciency increases strongly for the other two cations. This behaviour can be
explained by the forming of different species of aqueous solution for Cd ions have little
tendency to hydrolyze at pH values below 8, but above this values it tend to exist in hydroxo-
complex compound. Cd ions in fresh water at pH =6-8, it predominant in CdOH-, Cd(OH)2-,
Cd(OH)3-and Cd(OH)4- where these species capable to bind with the surface of the diatomite by
forming an electrostatic forces [21].
For Cu ions in the acidic medium, the predominant species are Cu2+, Cu(OH)º2, CuHCO3+,
CuCO3ºand CuOH-, which can formed some complex with the functions groups (carboxyl group)
on the surface of the diatomes. At the basic medium pH >10 the major species are Cu(OH)42-
and Cu(OH)3- which less active to form bonds [22].
For Co cations the optimum extraction by diatomite from its aqueous solution is nearly
in the natural medium (pH =6-8). This may explained by the presence of Co(OH)+ and Co(OH)2
species which allowing to the Co+ to be easily extracted onto the negatively charged diatomite
surface as pointed out by Shenget et al (23), who used the china diatomite in removing of Co
cations from the aqueous solutions
To study the effect of the initial concentration of the three cations on the efficiency of
removing by using diatomite, for different concentrations were prepared from each cations.
These concentrations are 5,10,15,20,25,ppm and 30 ppm, and the same weight of diatomite
was used. The filtrate after equilibrium attends was analyzed to calculate the effeciency. Fig 5,
represents the dependence of the removing efficiency on the initial concentrations of the
cations.

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510 15 20 25 30
0
10
20
30
40
50
60
70
80
90
100
110
effeciency(%)
initial concentration (ppm)
eff.ofCu
eff.ofCo
eff.ofCd
Figure 5: effect of the initial concentration on the effeciency of
removing cations
The obtained results indicate that the efficiency increases rapidly at low concentration
recording the maximum value for Cd=83, for Cu= 92 and Co= 85. After these values, the
effeciency of removing are nearly independent on the concentration, thus may due to the
saturation of the surface of diatomite [24]. It noteworthy that the dependence of the efficiency
on the concentrations of the cations behaves the same trend as observed by studing the pH
effect and following the same trend Cu>Cd=Co. Table 2 shows the data which illustrated the
trends of extraction.
Table 2: shows the data which illustrated the trends of extraction
cation
electro negativity
Ionic radius
Max efficiency
PH value
Cd
1.69
0.97
83%
8-10
Cu
1.9
0.73
92%
4-5.5
Co
1.9
0.74
85%
6-7
CONCLUSION
From the study of removing Cd, Cu, and Co from their aqueous solution by using
diatomite it may conclude that:-
(i) The main constituent of diatomite is amorphous silica with some other oxides with
specific surface area = 7.3 m2/g
(ii) The effeciency of removing depent markedly on the pH value and the initial
concentrations as well as the ionic species of each cation in their solution
(iii) The effeciency removing of the three cations behaves the following sequence Cd> Cu> Co
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