Kinetic Studies of Sorption Separation of Phosphorus with Usage of Sorbents on the Basis of Natural Clays

Introduction

The problem of environment protection is one of the most important problems today [1]. As waste is potential secondary material resources, the operating system of removal of technogenic waste leads to irrevocable loss of valuable secondary material resources, energy and land resources [2]. The production of sorbents [3]  and catalysts [4]  on the basis of clay raw materials restrains the fact that today influence of modifying on structural, thermal, adsorption and catalytic properties of such materials is insufficiently investigated. The main technogenic waste of phosphoric production are phosphorus sludge which are formed on phosphorus condensation stages [5-11]. In compliances with the modern representations, phosphorus sludge represents  phosphorus emulsion in water stabilized with fine-grained solids [12-13].

Considering phosphorus sludge as stabilized with highly active pollution of emulsion in water, the way of phosphorus separation  is chosen from sludge with usage of solid porous sorbents on the basis of natural refractory, bentonitic clays and vermiculites [14]. The processing of phosphorus sludge with sorption method provides high extent of phosphorus separation, and usage of native, available natural minerals allows to reach considerable economic and ecological effect for this purpose.

Materials and Methods

The experimental datas were processed with Rotinyan-Drozdov’s equation for definition of chemical process of phosphorus separation from phosphorus sludge with usage of sorbents on the basis of native silica-alumina clays.

where – M – efficient constant of speed process;

β –  drag coefficient

Rotinyan-Drozdov’s equation is used when studying heterogeneous processes and efficient specific reaction rate characterizes the processes beginning on all surface of the heterogeneous system. At the same time finding of drag coefficient defines influence of resultants  on the interaction speed process.

Studying of the kinetics of adsorption chemical process was carried out at temperatures of 60, 70, 80, 90°C with isothermal endurance 30, 60, 90, 120, 150 minutes with usage of sorbents on the basis of clays from Kazakhstan’s deposits Darbaza and Lenger and also vermiculite of the Kulandy field which is also located in South Kazakhstan.

Laboratory researches of phosphorus separation from sludge with usage of sorbents on the basis of native clays and  vermiculite were carried out on the installation given on the Figure 1.

The work was carried out on the installation which works according to the following scheme. The phosphorus sludge admits from the compressor 1 through a flow meter with the needle nozzle 2. Further it passes through water in the flask 3. The moisture content of air is measured with the sensor of the relative humidity 7. Passing the flask with absorber, cleaned gas with phosphorus is collected in the flask with water 4. Parameters of humidity and air temperature are displayed on digital devices TPM200 (6). The water temperature regulation is carried out in TC4S (9). Maximum withstand water temperature is 90°C.

Figure 1: Laboratory installation for adsorption process Click here to View figure

 

Results and discussion

The experimental data of the sorption of phosphorus sludge obtained on the laboratory installation are given in Figures 2-4. Dependences of extent of separation of phosphorus from temperature and time are defined on the residual content of phosphorus in the termination of adsorbed products.

Figure 2: The influence of temperature and durations of experiences on the extent of phosphorus separation from sludge with usage of bentonitic sorbents.   Click here to View figure

 

1 – t =60⁰C; 2 – t =70⁰C; 3 – t =80⁰C; 4 – t =90⁰C;

Figure 3: The influence of temperature and duration of experiences on the extent of phosphorus separation from sludge with usage of sorbents on the basis of refractory clays.   Click here to View figure

 

1 – t =60⁰C; 2 – t =70⁰C; 3 – t =80⁰C; 4 – t =90⁰C;

Figure 4: The influence of temperature and durations of experiences on the extent of phosphorus separation from sludge with usage of sorbents on the basis of vermiculites. Click here to View figure

 

1 – t =60⁰C; 2 – t =70⁰C; 3 – t =80⁰C; 4 – t =90⁰C;

The analysis of graphic data confirms direct dependence of extent of  phosphorus separation on the temperature and isothermal endurance of the process. The maximal extent of  phosphorus separation up to 98% is reached when using sorbents on the basis of the Darbaza clay modified with sulfuric acid 0,25M.

The experimental data of extent dependence of  phosphorus separation from phosphorus sludge with  various sorbents at the studied temperatures 80-90⁰C and duration  30 -150 minutes, mathematically processed with Rotinyan– Drozdov’s equation are presented in tables 1-3:

Table 1: Mathematical processing of experimental data with Rotinyan– Drozdov’s equation of  sorption of phosphorus sludge sorbents on the basis of Darbaza bentonitic clay Click here to View table

 

Table 2: Mathematical processing of experimental data with Rotinyan– Drozdov’s equation of  sorption of phosphorus sludge sorbents on the basis of Lenger (refractory) clays Click here to View table

 

Table 3: Mathematical processing of experimental data with Rotinyan– Drozdov’s equation of  sorption of phosphorus sludge sorbents on the basis of Kulantau vermiculite Click here to View table

 

On the basis of mathematical calculation data components of the Rotinyan– Drozdov’s equation are built graphic dependences

which are presented in figures 5-7.

Figure 5 Click here to View figure

 

Figure 6 Click here to View figure

 

Figure 7 Click here to View figure

 

The analysis of graphic dependences shows that the studied process is described well with Rotinyan–Drozdov’s equation that testifies rectification of the experimental curve dependences of extent of  phosphorus separation depending from various factors.

The drag coefficient β₁ β₂ β₃  is calculated on tg φ of each straight line. The efficient specific reaction rate for each temperature was defined from the schedule at

The activation energy defines influence of temperature on the speed process. In practice the calculation  “apparent” activation energy for the Arrhenius equation is widespread:

K = A_oe ^–E/RT                  (2)

where E – activation energy, kJ/mol.

As concentration of reactants does not depend on the temperature, the same ratio turns out also for the speed  process (V).

V = V_oe ^–E/RT                                                       (3)

That is the more than E the quicker reaction rate with temperature increasing E is defined from expression:

where 4.575 is the product of conversion factor from natural logarithm into decimal 2.303 and universal gas constant R 1.9865 [kal/Mol∙K]

From graphic dependences of ln

(Fig. 8-10) given for each type of sorbents were calculated values of apparent activation energy (Е app.), which results are given in the table of indexes:

Table 4: Value E each for different types of sorbents

№	Name of  the sorbent	Drag coefficient at T		кJ/mol
		0С	β
1	Darbaza clay	60	0,007	83,14
		70	0,015
		80	0,028
		90	0,039
2	Kulantau vermiculite	60	0,02	2,078
		70	0,04
		80	0,06
		90	0,08
3	Lenger clay	60	0,03	0,29
		70	0,05
		80	0,07
		90	0,08

 

The graph of dependence of ln

is presented in Figures 8-10.

Figure 8 Click here to View figure

 

Figure 9 Click here to View figure

 

Figure 10 Click here to View figure

 

Conclusions

The analysis of the obtained values of E app. extents of  phosphorus separation from the type of the sorbent show that the maximal extent of  phosphorus separation is reached when using sorbents on the basis of Darbaza clay. “Apparent” activation energy has maximal value 83,14 KJ/mol, the drag coefficient β reaches 0,07 – 0,039 that demonstrates course of process of the sorption phosphorus from sludge in transient regime with considerable influence of diffusion factors. The sorption process at using Lenger clay and Kulantau vermiculite is characterized with E app from 0,29 to 2,078 KJ/mol that corresponds about course of process in diffusion area.

Acknowledgments

The work was financially supported by a project GF 68-31 of the Ministry of Education and Science of the Republic of Kazakhstan

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