266
solutions was adjusted using 0.1M HCl or 0.1M HNO 3 and 0.1M NaOH. All
reagents and chemicals used in the experiments are of analytical grade.
The quantitative monitoring of the dynamics of studied system regarding the
presence of Cr(VI) ions in the model solutions was performed with the atomic
absorption spectrophotometric (AAS) method using AAC PerkinElmer model
AA700 and UV-Vis spectrophotometric analysis instrument type HACH DR/2010.
In order to determine the mass loss and the characteristic points of possible physical and/or chemical changes occurring in the materials tested in the temperature
range which is examined, thermogravimetric and differential thermal analyses
(TGA/DTA) were performed. Test apparatus used during this analysis was
PerkinElmer Pyris Diamond thermogravimetric/differential thermal analyzer, in air
conditions, at rate of heating of 10 °C/min, using 15 mg of sample.
The specific surface area was conducted by the BET method for N 2 adsorption.
Determination of the point of zero charge of clayey diatomite was conducted by
adding 0.2 g diatomite in Erlenmeyer flasks (300 ml) and adding 100 ml of distilled
water with pH (pH initial ) from 2 to 10. pH is adjusted by adding solution of HCl or
NaOH as required. Erlenmeyer flasks were continuously mixed on stirrer (140 rpm)
for 24 hours at room temperature. The suspension was then filtered and the pH (pH final ) of every filtrate was determined. The pH of the solutions was measured by pH
meter GMH 3500 series, Greisinger, Germany.
9.2.1 Adsorption Experiment
In order to define the adsorption characteristics or adsorption affinity and capacity,
the raw material was tested in the direction of separating of Cr(VI) ions from model
aqueous solutions, as well as monitoring the dynamics of the studied process; a
series of batch adsorption experiments were performed. These experiments were
conducted in the laboratory glass reactor with a working volume of 2 l, equipped
with a magnetic stirrer at room temperature and constant speed of stirring at
400 rpm, while monitoring the equilibrium and the kinetics of the process. During
the experiments, the influence of the following operating parameters on the process
of removal of Cr(VI) ions was studied: initial concentration of adsorbate (0.3, 0.4,
0.5, and 0.6 mg/l), time of adsorption (5–180 min), and the amount of adsorbent
(0.5–5.5 g/l). The pH of the solutions was 3. For the preparation of standard solutions with the desired initial metal concentration, a standard solution of K 2 Cr 2 O 7
was used.
The values of initial concentrations of the working adsorbent are selected in a
given operating range based on the MPL statutory regulation values for drinkable
and wastewaters with heavy metals multiple times over the allowed limit. Thus, this
covers the areas of potential pollutants of water resources that would originate from
geogenic or anthropogenic origin. The results of the experiments are used to modulate the equilibrium of the adsorption process through the implementation of several
adsorption isotherms (Langmuir, Freundlich, Langmuir-Freundlich, and
H. Memedi et al.
solutions was adjusted using 0.1M HCl or 0.1M HNO 3 and 0.1M NaOH. All
reagents and chemicals used in the experiments are of analytical grade.
The quantitative monitoring of the dynamics of studied system regarding the
presence of Cr(VI) ions in the model solutions was performed with the atomic
absorption spectrophotometric (AAS) method using AAC PerkinElmer model
AA700 and UV-Vis spectrophotometric analysis instrument type HACH DR/2010.
In order to determine the mass loss and the characteristic points of possible physical and/or chemical changes occurring in the materials tested in the temperature
range which is examined, thermogravimetric and differential thermal analyses
(TGA/DTA) were performed. Test apparatus used during this analysis was
PerkinElmer Pyris Diamond thermogravimetric/differential thermal analyzer, in air
conditions, at rate of heating of 10 °C/min, using 15 mg of sample.
The specific surface area was conducted by the BET method for N 2 adsorption.
Determination of the point of zero charge of clayey diatomite was conducted by
adding 0.2 g diatomite in Erlenmeyer flasks (300 ml) and adding 100 ml of distilled
water with pH (pH initial ) from 2 to 10. pH is adjusted by adding solution of HCl or
NaOH as required. Erlenmeyer flasks were continuously mixed on stirrer (140 rpm)
for 24 hours at room temperature. The suspension was then filtered and the pH (pH final ) of every filtrate was determined. The pH of the solutions was measured by pH
meter GMH 3500 series, Greisinger, Germany.
9.2.1 Adsorption Experiment
In order to define the adsorption characteristics or adsorption affinity and capacity,
the raw material was tested in the direction of separating of Cr(VI) ions from model
aqueous solutions, as well as monitoring the dynamics of the studied process; a
series of batch adsorption experiments were performed. These experiments were
conducted in the laboratory glass reactor with a working volume of 2 l, equipped
with a magnetic stirrer at room temperature and constant speed of stirring at
400 rpm, while monitoring the equilibrium and the kinetics of the process. During
the experiments, the influence of the following operating parameters on the process
of removal of Cr(VI) ions was studied: initial concentration of adsorbate (0.3, 0.4,
0.5, and 0.6 mg/l), time of adsorption (5–180 min), and the amount of adsorbent
(0.5–5.5 g/l). The pH of the solutions was 3. For the preparation of standard solutions with the desired initial metal concentration, a standard solution of K 2 Cr 2 O 7
was used.
The values of initial concentrations of the working adsorbent are selected in a
given operating range based on the MPL statutory regulation values for drinkable
and wastewaters with heavy metals multiple times over the allowed limit. Thus, this
covers the areas of potential pollutants of water resources that would originate from
geogenic or anthropogenic origin. The results of the experiments are used to modulate the equilibrium of the adsorption process through the implementation of several
adsorption isotherms (Langmuir, Freundlich, Langmuir-Freundlich, and
H. Memedi et al.