Junya Kano, Qiwu Zhang, Fumio Saito, Michel Baron* and Ange Nzihou*
IMRAM, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
* Ecole des Mines d'Albi, Campus Jarlard, 81013 Albi Cedex 09, France
Abstract
Polyvinyl chloride (PVC) is an excellent polymer, because of its chemical stability. This enables us to use it in wide application to different fields. After their usage, proper treatment has to be made, and when it is burned out in a furnace without any temperature control, toxic gases and substances are generated. Therefore, safety treatment of the PVC waste is necessary. We have developed a non-thermal process for dechlorinating of PVC, and this process is composed of two steps: The first step is to grind the PVC waste with an active grinding additive such as CaO, leading to transformation of organic chlorine into water soluble chloride mechanochemically. The second step is to remove the formed chloride from the milled product by washing with water. The solid residue after filtration has already been dechlorinated, so that it can be recycled as a safety fuel.
When the filtrate is mixed with solution, which includes (PO
4
2), then hydroxy-apatite (HAp) fine particles are formed. It has been found that the precipitate (HAp) formed has a special absorption capacity for heavy metals such as Pb and Zn. Therefore, this filtrate can also be recycled as a useful chemical for cleaning environment in rivers and a like.
Polyvinyl chloride (PVC) is well known and widely used as not only commodities but also industrial materials in construction, agriculture, medical fields and a like, since it has properties of good chemical stability and is relatively low cost. After usage of the PVC products, they should be disposed adequately. Recently, three disposal methods for PVC waste have been proposed: 1) The first method is to use as a raw material for blast furnace [1] , 2) the second one is to use as a fuel for kiln in cement processes [2] , 3) the third one is to use as a source for liquefying technology [3,4] . These are all excellent, however, we would consider more about some drawbacks such as operational cost and maintainance of the equipments.
The authors have proposed an alternative and novel process for dechlorinating a PVC waste by its grinding with a reagent such as CaO followed by water rinsing [5,6] . The grinding causes mechanochemical reaction between
PVC and CaO, forming soluble CaOHCl. The CaOHCl can be removed from the product by washing with water, so that this process obliges to emit an enormous amount of waste water including CaOHCl when CaO is used as a reagent in the grinding with PVC. This suggests that hydroxyapatite (HAp, Ca
10
(PO
4
)
6
(OH)
2
), which is one of the most attractive materials for absorbing heavy metals such as Zn, Cd and Pb [7-9] , would be formed from the waste water when it is mixed with liquid including PO
4
3. As for the solid residue after filtration of the ground product, most of chlorine has been removed, so that it could be used as a safety fuel.
The main purpose of this paper is to propose pre-treatment of PVC wastes by a mechanochemical method and their Recycle.
A PVC powder sample used in this experimental was a chemical reagent (Wako Chemical Co., Ltd., Japan), and its initial mean particle diameter is about 133
 m. Polymerization degree of the sample is about 1100. CaO was prepared by heating calcium hydroxide (Ca(OH)
2
) powder at 800
℃
, and its mean particle diameter is about
1.8
 m. The PVC sample was mixed with the CaO one so as to be equi-molar ratio of CaO to Cl in the PVC sample, and the mixture of 3g was subjected to grinding in air by using a planetary ball mill (P-7, Fritsch,
Germany). The mill is composed of a pair of pot having 50ml in volume. The speed ratio of revolution to rotation of the mill was fixed at 1, and the speed was set at 700rpm. The grinding period of time was varied up to

12 hours, and the ground product was removed thoroughly from the pot after grinding. The ground product of 1g was dispersed in distilled water by stirring for 1 hour to dissolve soluble compound formed mechanochemically in the product, subsequently, it was filtered to separate filtrate from the solid. Total volume of the filtrate was set at 250ml.
A method for formation of HAp fine particles is as follows: first of all, Na
3
PO
4
solution was prepared by diluting 0.83g of Na
3
PO
4
into distilled water, and its volume was set at 250ml. Then the Na
3
PO
4
solution was mixed with the filtrate at the same volume in an ambient air. pH value in the Na
3
PO
4
solution was measured as
11.8 and that in the solution after mixing with the filtrate was 11.7.
The samples were characterized by X-ray diffraction (XRD) analysis (Rigaku, RAD-B system, Cu-K

), and the concentration of chemical species in the solution was determined by an ion chromatograph (IC) (LC10 series,
Shimadzu Co. Ltd.). The experimental procedure is shown in Figure 1 .
Figure 1 Flow chart of the sample preparation of and the characterization
Figure 2 shows XRD patterns of the PVC-CaO mixtures ground for various periods of grinding time. The intensity of peaks corresponding to CaO is decreasing with an increase in the grinding time. New peaks, which are corresponding to CaOHCl, appear after 6-hour grinding, and their intensities go up. This indicates that mechanochemical reaction between PVC and CaO took place, and that CaOHCl formed as monomer expression given by Eq.(1):
[CH
2
CHCl] + CaO

CaOHCl + [CH=CH] (1)
According to the previous work [5], the double bonds in the ground product have been confirmed. It is clearly observed from the pattern of the solid residue after filtration that CaOHCl in the product has been removed by washing with water, being concentrated in the filtrate ( Figure 3 ). The peaks of CaCO
3
are observed in Figure 3, due to the carbonation of unreacted CaO during washing with water.
Figure 4 shows two XRD patterns of solid particles formed in the solution after mixing the two solutions of the filtrate including CaOHCl and the Na
3
PO
4
solution. One is the particles dried in air (A) and the other the dried one heated at 100 0 C in an oven (B). It is difficult to identify the particles (A) dried in air to be
HAp, while the particles (B) dried in the oven is identified as HAp. It is therefore conformed that the composition of solid particles formed from the solution is HAp, and the total reaction between the two components in the solution is given as follows:
10CaOHCl (l) + 6Na
3
PO
4
(l) = Ca
10
(PO
4
)
6
(OH)
2
(s) + 10NaCl (l) + 8NaOH (l) (2)

●
●
CaO
△
CaOHCl
●
△
△
△
△
△
△
△
10 20 30 40


50
Figure 2 XRD patterns of samples ground for various periods of time
■
CaCO
3
■
■
■ ■ ■
10 20 30 40


50

Figure 5 shows an undersized cumulative size distribution curve of HAp particles dried in air. A SEM photograph of the HAp particles dried at 100 0 C in an oven was superimposed in this figure. The curve clearly shows that the size of particles ranges from about 1 to 100
 m and the mean particle size is about 15
 m. Thus,
CaOHCl in the wastewater emitted from the mechanochemical dechlorination process of PVC using CaO as a reactant can react with PO
4
3, forming HAp fine particles in the solution. It would be useful when the waste water is used for reducing the concentration of PO
4
3 in rivers, lakes and a like. The hydroxyapatite shows very high removal capacity for divalent heavy metals ions. It can be used for the decontamination of waste water containing such ions.
●
Ca
10
(PO
4
)
6
(OH)
2
●
●
●
●
●
●
(B) drying in oven for 1 day
●
●
●
(A) drying in air for 1 day
10 20 30
2

(degree,CuK

)
40 50
100
(A) in air and (B) in oven at 100
℃
80 mean particle size : 15.5
 m
60
40
20
0
0.1
1 10
Particle size /
 m
100 1000 o C
60
 m
Figure 5 Size distribution curve and SEM photograph of HAp.

A non-thermal process for dechlorinating polyvinyl chloride (PVC) has been introduced in this paper, and this process is composed of two steps: one is to grind the PVC waste with CaO, and the second one is to remove the formed chloride from the milled product by washing with water. The solid residue after filtration has already been dechlorinated, so that it can be recycled as a safety fuel. The filtrate can be used as a chemical for reducing
(PO
4
2) in rivers and a like, because hydroxy-apatite (HAp) fine particles are formed. It has a special absorption capacity for heavy metals such as Pb and Zn. Therefore, this filtrate can also be recycled as a useful chemical for cleaning environment in rivers and a like. The crystallinity of the HAp particles dried in air is not well, but it is improved by drying at 100 o C. The mean particle size of the formed HAp fine particles is about 15
 m.
References
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