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Effect of Particle Size Distribution on Leaching Properties of Building Materials
Waste Matertolr in CfJncfrUCliim.
J . J . J . R . Gournans. H . A van der Sluut ond Th G .4alberr /Editor.\/ '01991 Elsevier Science Piihlrslier~8.V . ,411 rryhrJ reserved.
283
EFFECT OF PARTICLE SIZE DISTRIBUTION ON LEACHING PROPERTIES OF BUILDING MATERIALS D. GOETZ and W. GdSEKER Institute of Soil Science, Allendeplatz 2, 2000 Hamburg 13 (Germany)
SUMMARY Particle s i z e d e p e n d e n t l e a c h i n g b e h a v i o u r o f 2 building recycling materialswere investigated. The resultsare showing, thata decrease of particle size is not automatically connected with an increase of the total surface area. There is a good correlation between surface area and amount of components leached. 1. INTRODUCTION
Secondary building materials for road construction can have variable particle size distributions. The particular fractions often are containing a distinct material composition. Following the view of governemental authorities, a test of grained material is preferred to simulate a worst - case scenario for leaching of contaminants. On theotherhand, an investigation of unaltered samples is preferred by the users of these building materials. The tests should be adapted to the distinct building materials and practical conditions to get an objective examination for materials. The alteration of particle size distribution during sample preparation is o f t e n d i s c u s s e d c o n t r o v e r s e l y . Toobtain adatabasis for leaching of distinct particle size fractions, different building materials were used for a column and a shaking test, which are representing two various leaching mechanisms. 2. MATERIALS
The following materials were used for the leaching tests: - Cement-stabilized fly-ash , composed with 78,14 % by weight, coal fly-ash cement PZ 35F 6,25 % - ' I water 15,61 % -'IThe material was stored for
4
month after setting.
284
- Secondarybuilding material (debris), containing bricks, clinker, tiles and conrete with remains of mortar. The materials were crushed into pieces < 10 mm, dried at 1 0 5 ° C for 24 hours. The driedmaterialwas sievedtogainthe follwingparticle size fractions: 10 - 6 , 3 mm o,a - 0,4 mm 6,3 - 2,O mm 0,4 - 0,l mm 2,o - o,a mrn < 0,l mm 3 . METHODS
Four tests were used for leaching the several particle size fractions of the two examined materials: - The regular g erman shaking test (DEV 54) using a liquid to solid ratio (L/S) of 10 and 3 replicates. - Column - test: Upstream percolation through a PVC - tube, length 20 cm and 5 cn diameter, using a vessel mounted into the circuit for compensation. The leachate was circulating at a speed of 30 ml/min for 24 hours. Similar to the shake - test, the materials were leached with a L/S ratio of 10 and 3 replicates. - Leaching with Ammoniumacetate for examination of exchangeable cations: 10 g material, used in a column - test with a L/S of 3 , was extractet for 4 times over a total time of 13 hours with a pH 7 Ammoniumacetate solution. The L/S ratio of this test was 20 and 3-5 replicates were conducted. Total concentrations were determined after hydrolysis with nitric acid, HF and boric acid. Total surface area was determined by Fa. Strohlein, using the BET Method. 4. RESULTS AND DISCUSSION The experiments showed interesting relationshipsbetweenparticle size distribution and leaching. The dependence of some leaching parameters from the particle size and surface area are presented in Fig 1 - 7 and 9 - 10. The replicates of the experiments are showing a good conformity, Therefor it could be said that random effects are playing a minor role.
285
The leachate pH ofthedistinct particle size fractions is varying within one pH grade and resulting in a characteristical pH curve for each material (Fig. la,b). In the column test, the leachate pH of debris (HBS) is increasing from the largest particle size fraction ( > 6,3 mm) to the 2-0,8 mm particles, declining in the next fraction and rising with the smaller particles again. In contrast to that, leachate pH of the shaking test is decreasing with the smaller particle size fractions. The corresponding curves ofthe fly ash cement (FAZ) are analogous to H B S , but the maximum pH was observed in the 0,8-0,4 mm fraction and there was no pH increase in the leachates out of the smaller fractions. The curves of shaking test leachates are comparable to the HBS material. Leachate conducticity of both tests are presented in Fig 2a,b. Column - tests are also showing maxima curves with the highest conductivity in the 2-0,Emm (HBS) and the 0,8-0,4mm (FAZ) fraction respectively. The Ca content (Fig. 3a,b) is comparable with the conductivity curves because Calcium is a dominant ion in the leachates of both materials. But the maxima of the column test are less distinct and the leachates of the shaking test are showing no (HBS) or slight (FAZ) increase of ca concentration. The concentrations of well soluble Na- and K salts (Fig. 4a,b and 5a,b) are lower by a factor of 10. Therefor they are playing a minor role in leachate element composition. The same can be mentioned for the heavy metals. To give an example for these elements, the Chromium concentrations are presented in Fig 6a,b. TheNa, KandCrconcentrations of HBSleachates obtained incolumn and shake tests are increasing with decreasing particle size, as expected. OppositetoHBS, the corresponding figures of FAZ are showing a clear maximum curve with the highest values at the 0,8-0,4 mm fraction.
-
286
>6,3 6,3-2,02,O-0,80,8-0,40,4-0,l<0,1
>6,3 6,3-2,0 2,O-0,80,8-0,40,4-0,l<0,1
particle size (mm)
particle size (mm) FA2
HBS 2500
6 .
2000
1600
2 1500
21400
v)
v)
.-
.-
Y 0)
Y 0
g .- 1000 3
g 1200
.-c0
0 ..c
500
0
>c
Fig. 2b
-
6 . R
1800
Fig. 2a
---
6,3-2,02,O-0,80,8-0,40,4-0,l
particle size (rnm) HBS
3
1000
800 >6
I
I
-I
I
6,3-2,'O2,O-0,80,8-0,40,4-0,l<0,'1
particle size (rnm) FAZ
pH (Flg.la,b) and conductivity (Flg.Pa,b) of shake-test (
-
1
and column-test ( - - - c - - )for debrls (HBS) and fly-ash-cement (FAZ)
287
1
b
-,.
*c
$ 1 140
>6,3 6.3-2,0 2,O-0,8 0,8-0,4 0,4-0,lC0,l
>6,3 6.3-2,0 2,O-0,8 0,8-0.4 0,4-0,lc0,l
particle size (mm) FAZ
particle size (mm)
HBS
20
. h
15
v
m
a
z
z
10
20
-
.
a
b
10 -'
5
0
-
\-,-T-
I
1
>6,3 6,3-2,0 2,0-0.8 0,8-0,4 0,4-0,l<0,1
1
1
-
-
particle size (mm) FA2
particle size (mm) HBS
Ca-concentrations (Fig.3a,b) and Na-concentrations (Flg.4a,b) of shaking-test ( column-test ( - - - o -) and NH4 Ac-solution after extraction ( for debris (HBS)and fly-ash-cement (FAZ)
-
>6,3 6,3-2,0 2,O-0.8 0,8-0.4 0,4-0,l<0,1
b
)
-
)
7
288
35
30
. =
25
L Y
20
b
a
15 10
6oj.
5
50 >6,3 6,3-2,0 2,O-0,8
0.8-0,4 0,4-0,l <0,1
;1
: I
I >6,3 6,3-2,0
particle size (mm) HBS
2.0-0,8
I I I 0,8-0,4 0,4-0,l
particle size
(mm)
FAZ
"'j
Fig. 6b
0,25 -
0,1
>6,3 6,3-2,0
particle size (mm) HBS
2,O-0.8 0,8-0,4 0,4-0,l < C
particle size (rnm) FAZ
K-concentrations (Fig.5a,b) and Cr-concentrations (Fig.6a,b) of shaking-test ( column-test ( . - 0 -) and NH4 Ac-solution after extraction ( for debris (HBS) and fly-ash-cement (FAZ)
)
-
1
289
Cation exchange capacity (CEC) curves of H B S and FAZ particle size fractions (Fig. 7) show the same shape like the above mentioned figures, CEC of HBS material increases from 4 0 to 130 mmol/kg with decreasing particle size and the CEC of FAZ show a maximum of 2 0 0 mmol/kg at the 0,8-0,4 mm fraction. The ionconcentrations intheAmmoniumacetate solutions (Fig. 3 - 6 ) after extraction can be parallelized with the element concentrations mentioned before except for Chromium. Although the Ammoniumacetate treatment of the material occured after leaching in a column - test, it is likely, thatnotonlyexchangeable ionsbutalso remainingsalts were soluted. This effect is clear visible by the large amount of Ammoniumacetate - mobilized Ca ions, which exceed the total CEC by several times. The total surfaces of the particular particle size fractions are presented in Fig 8. As we expected, the surface area of the HBS materials is increasing with decreasing particle size. But FAZ is showing a maximum in the 0 , 8 - - 0 , 4 mm fraction. For comparison, surfaces of basalt particle size fractions were determined. In this case, surface area is increasing until a particle size of 2-0,8 mm. Then, this curve shows a minimum at the 0 , 8 - 0 , 4 mm fraction. The results of our experiments were a bit surprising. It is visible, that some parameters as pH, conductivity and solubility of Ca are determinedby the chosen leachingprocedures. Eachtestshowed complete differentcurves. Inoppposite, the compositionofthematerial plays a minor role. Particle size analyses of material, which are used in a shaking test, indicated that mechanical abrasion led to a disintegration of sample particles. This effect was notable seen from the coarser particles. However, leaching behaviour of Cr, Na and K was not influenced by the grinding effect of the shaking test. These Elements show nearly the same solubility in column- and shaking tests. But there ist a difference between the particle size dependent curves when both examined materials are regarded. Due to heterogeneous composition ofthe material, consisting of several compounds as mortar,
290 250
12000-
Fig. 7
Fig. 8
200 0
E
P
z 0
150
:
Yu
100
50
0
I I I 2,O-0,8 0.8-0,4 0,4-0,l
I 6,3-2,0
>6
>6,3
2,O-0,8 0,8-0,4 0.4-0,lc O , ~
6,3-2,0
particle size (mm)
particle size (mm)
debris (HBS)
fly-ash-cement (FAZ)
r ..u..
A
0,0007
Fig.9
0,0006
:*. .... ,.,
0,0005-
......
-
.......-.
L,.
0,0002
i
0,0001
0,15 -
p...’”
N
-F
0
.......... 9...........
o,...
-c
.....a
...... ,L1..‘
0,l-
m
, ,+,
z
x-
,’.,..
r _ _ _ l , ’
>6,3
6,3-2,0 2,O-0,8 0,8-0,40,4-0,l<0,1
>6,3
2,O-0,8 0,8-0,40,4-0,l<0,1
6,3-2,0
particle size (mm) column-test
particle size (mm) column-test
fly-ash-cement (FAZ),
K
Na
Cr
...
0
- @ .
debris (HBS): K
Na
Cr
-c.
-c.
-L-
29 1
bricks or cement, a rather unsteady concentration curve of HBS leachates was expected. But a continuous increase of Cr, Na and K concentrations with decreasing particle size was detected. Opposite tothe HBS material, leaching of particle size fractions of the very homogeneous FAZ was resulting in Cr, Na and K concentration curves with a maximum in the 0 , 4 - 0 , 0 nun fraction. The same shape is visible from figures which show the dependence of CEC from particle size. By regarding our results avaiable up to now, this coincidence can be explained with the fact that the elements were in an exchangeable state before leaching out of the investigated materials. Change of CEC with particle size can be explained with the total surface area, whose curve show the same shape. Taking the value for the theoretic spherical surface as basis, an expotential increase of total surface can be expected. Leachate analyses of the HBS material were fulfilling these expectations. Decrease of total surfaces of particle size fractions 0 , 4 - 0 , 4 mm and < 0,lmm of FAZ can only be explained by chemical transformations ash is consisting to the on surfaces of the fine particles. Fly greater extend of small glazed globules which can be destroyd in the fine fractions. With that, new reactive surfaces were formed which lead to a agglutination of the filigree structure elements. In this way, the avaiable inner surfaces could have been reduced. Chemical transformations at particles surfaces are probable, because the particle size dependent pH values of this homogenous material are showing relatively strong variations. The strong variations of particle size dependent HBS leachate pH canbemost easily explainedwith inhomogenous distribution of material in the distinct particle size fractions. There seems to be less influence of the high pH values on the leaching behaviour of the examined materials. A coincidence ist only visible between pH and electric conductivity of the FAZ. The experiments are showing that there are no simple relations between particle size and leaching parameters. Even total surface is not automatically increasing with decreasing particle size. This phenomenon is even visible at a apparent homogenous and pore - free
-
292
material like basalt. Also, there can be a particle size dependent mobilization of the elements to be investigated. E.g. a liniear liberation of Sulfate with decreasing FAZ particle size or a maximum curve, describing the KandNa - c o n t e n t o f F A Z l e a c h a t e w a s detected. Other investigations, dealing with the particle size dependent leaching cf steel-works slag, lead to a miniumum curve for Vanadium and an increase of Chromium with decrease of particle size. But these experiments show that the total surface of the materials is often determining the leaching of elements. The surface to amount of element leached - ratio is nearly equal for all particle size fractions (Fig. 9,lO). This means under the aspects of practical uses, that grinding of sample material must not lead automatically to a increasedleaching. A convention for the particle sizes to be investigated is useful to assure a comparability of different materials.
J . J . J . R . Gournans. H . A van der Sluut ond Th G .4alberr /Editor.\/ '01991 Elsevier Science Piihlrslier~8.V . ,411 rryhrJ reserved.
283
EFFECT OF PARTICLE SIZE DISTRIBUTION ON LEACHING PROPERTIES OF BUILDING MATERIALS D. GOETZ and W. GdSEKER Institute of Soil Science, Allendeplatz 2, 2000 Hamburg 13 (Germany)
SUMMARY Particle s i z e d e p e n d e n t l e a c h i n g b e h a v i o u r o f 2 building recycling materialswere investigated. The resultsare showing, thata decrease of particle size is not automatically connected with an increase of the total surface area. There is a good correlation between surface area and amount of components leached. 1. INTRODUCTION
Secondary building materials for road construction can have variable particle size distributions. The particular fractions often are containing a distinct material composition. Following the view of governemental authorities, a test of grained material is preferred to simulate a worst - case scenario for leaching of contaminants. On theotherhand, an investigation of unaltered samples is preferred by the users of these building materials. The tests should be adapted to the distinct building materials and practical conditions to get an objective examination for materials. The alteration of particle size distribution during sample preparation is o f t e n d i s c u s s e d c o n t r o v e r s e l y . Toobtain adatabasis for leaching of distinct particle size fractions, different building materials were used for a column and a shaking test, which are representing two various leaching mechanisms. 2. MATERIALS
The following materials were used for the leaching tests: - Cement-stabilized fly-ash , composed with 78,14 % by weight, coal fly-ash cement PZ 35F 6,25 % - ' I water 15,61 % -'IThe material was stored for
4
month after setting.
284
- Secondarybuilding material (debris), containing bricks, clinker, tiles and conrete with remains of mortar. The materials were crushed into pieces < 10 mm, dried at 1 0 5 ° C for 24 hours. The driedmaterialwas sievedtogainthe follwingparticle size fractions: 10 - 6 , 3 mm o,a - 0,4 mm 6,3 - 2,O mm 0,4 - 0,l mm 2,o - o,a mrn < 0,l mm 3 . METHODS
Four tests were used for leaching the several particle size fractions of the two examined materials: - The regular g erman shaking test (DEV 54) using a liquid to solid ratio (L/S) of 10 and 3 replicates. - Column - test: Upstream percolation through a PVC - tube, length 20 cm and 5 cn diameter, using a vessel mounted into the circuit for compensation. The leachate was circulating at a speed of 30 ml/min for 24 hours. Similar to the shake - test, the materials were leached with a L/S ratio of 10 and 3 replicates. - Leaching with Ammoniumacetate for examination of exchangeable cations: 10 g material, used in a column - test with a L/S of 3 , was extractet for 4 times over a total time of 13 hours with a pH 7 Ammoniumacetate solution. The L/S ratio of this test was 20 and 3-5 replicates were conducted. Total concentrations were determined after hydrolysis with nitric acid, HF and boric acid. Total surface area was determined by Fa. Strohlein, using the BET Method. 4. RESULTS AND DISCUSSION The experiments showed interesting relationshipsbetweenparticle size distribution and leaching. The dependence of some leaching parameters from the particle size and surface area are presented in Fig 1 - 7 and 9 - 10. The replicates of the experiments are showing a good conformity, Therefor it could be said that random effects are playing a minor role.
285
The leachate pH ofthedistinct particle size fractions is varying within one pH grade and resulting in a characteristical pH curve for each material (Fig. la,b). In the column test, the leachate pH of debris (HBS) is increasing from the largest particle size fraction ( > 6,3 mm) to the 2-0,8 mm particles, declining in the next fraction and rising with the smaller particles again. In contrast to that, leachate pH of the shaking test is decreasing with the smaller particle size fractions. The corresponding curves ofthe fly ash cement (FAZ) are analogous to H B S , but the maximum pH was observed in the 0,8-0,4 mm fraction and there was no pH increase in the leachates out of the smaller fractions. The curves of shaking test leachates are comparable to the HBS material. Leachate conducticity of both tests are presented in Fig 2a,b. Column - tests are also showing maxima curves with the highest conductivity in the 2-0,Emm (HBS) and the 0,8-0,4mm (FAZ) fraction respectively. The Ca content (Fig. 3a,b) is comparable with the conductivity curves because Calcium is a dominant ion in the leachates of both materials. But the maxima of the column test are less distinct and the leachates of the shaking test are showing no (HBS) or slight (FAZ) increase of ca concentration. The concentrations of well soluble Na- and K salts (Fig. 4a,b and 5a,b) are lower by a factor of 10. Therefor they are playing a minor role in leachate element composition. The same can be mentioned for the heavy metals. To give an example for these elements, the Chromium concentrations are presented in Fig 6a,b. TheNa, KandCrconcentrations of HBSleachates obtained incolumn and shake tests are increasing with decreasing particle size, as expected. OppositetoHBS, the corresponding figures of FAZ are showing a clear maximum curve with the highest values at the 0,8-0,4 mm fraction.
-
286
>6,3 6,3-2,02,O-0,80,8-0,40,4-0,l<0,1
>6,3 6,3-2,0 2,O-0,80,8-0,40,4-0,l<0,1
particle size (mm)
particle size (mm) FA2
HBS 2500
6 .
2000
1600
2 1500
21400
v)
v)
.-
.-
Y 0)
Y 0
g .- 1000 3
g 1200
.-c0
0 ..c
500
0
>c
Fig. 2b
-
6 . R
1800
Fig. 2a
---
6,3-2,02,O-0,80,8-0,40,4-0,l
particle size (rnm) HBS
3
1000
800 >6
I
I
-I
I
6,3-2,'O2,O-0,80,8-0,40,4-0,l<0,'1
particle size (rnm) FAZ
pH (Flg.la,b) and conductivity (Flg.Pa,b) of shake-test (
-
1
and column-test ( - - - c - - )for debrls (HBS) and fly-ash-cement (FAZ)
287
1
b
-,.
*c
$ 1 140
>6,3 6.3-2,0 2,O-0,8 0,8-0,4 0,4-0,lC0,l
>6,3 6.3-2,0 2,O-0,8 0,8-0.4 0,4-0,lc0,l
particle size (mm) FAZ
particle size (mm)
HBS
20
. h
15
v
m
a
z
z
10
20
-
.
a
b
10 -'
5
0
-
\-,-T-
I
1
>6,3 6,3-2,0 2,0-0.8 0,8-0,4 0,4-0,l<0,1
1
1
-
-
particle size (mm) FA2
particle size (mm) HBS
Ca-concentrations (Fig.3a,b) and Na-concentrations (Flg.4a,b) of shaking-test ( column-test ( - - - o -) and NH4 Ac-solution after extraction ( for debris (HBS)and fly-ash-cement (FAZ)
-
>6,3 6,3-2,0 2,O-0.8 0,8-0.4 0,4-0,l<0,1
b
)
-
)
7
288
35
30
. =
25
L Y
20
b
a
15 10
6oj.
5
50 >6,3 6,3-2,0 2,O-0,8
0.8-0,4 0,4-0,l <0,1
;1
: I
I >6,3 6,3-2,0
particle size (mm) HBS
2.0-0,8
I I I 0,8-0,4 0,4-0,l
particle size
(mm)
FAZ
"'j
Fig. 6b
0,25 -
0,1
>6,3 6,3-2,0
particle size (mm) HBS
2,O-0.8 0,8-0,4 0,4-0,l < C
particle size (rnm) FAZ
K-concentrations (Fig.5a,b) and Cr-concentrations (Fig.6a,b) of shaking-test ( column-test ( . - 0 -) and NH4 Ac-solution after extraction ( for debris (HBS) and fly-ash-cement (FAZ)
)
-
1
289
Cation exchange capacity (CEC) curves of H B S and FAZ particle size fractions (Fig. 7) show the same shape like the above mentioned figures, CEC of HBS material increases from 4 0 to 130 mmol/kg with decreasing particle size and the CEC of FAZ show a maximum of 2 0 0 mmol/kg at the 0,8-0,4 mm fraction. The ionconcentrations intheAmmoniumacetate solutions (Fig. 3 - 6 ) after extraction can be parallelized with the element concentrations mentioned before except for Chromium. Although the Ammoniumacetate treatment of the material occured after leaching in a column - test, it is likely, thatnotonlyexchangeable ionsbutalso remainingsalts were soluted. This effect is clear visible by the large amount of Ammoniumacetate - mobilized Ca ions, which exceed the total CEC by several times. The total surfaces of the particular particle size fractions are presented in Fig 8. As we expected, the surface area of the HBS materials is increasing with decreasing particle size. But FAZ is showing a maximum in the 0 , 8 - - 0 , 4 mm fraction. For comparison, surfaces of basalt particle size fractions were determined. In this case, surface area is increasing until a particle size of 2-0,8 mm. Then, this curve shows a minimum at the 0 , 8 - 0 , 4 mm fraction. The results of our experiments were a bit surprising. It is visible, that some parameters as pH, conductivity and solubility of Ca are determinedby the chosen leachingprocedures. Eachtestshowed complete differentcurves. Inoppposite, the compositionofthematerial plays a minor role. Particle size analyses of material, which are used in a shaking test, indicated that mechanical abrasion led to a disintegration of sample particles. This effect was notable seen from the coarser particles. However, leaching behaviour of Cr, Na and K was not influenced by the grinding effect of the shaking test. These Elements show nearly the same solubility in column- and shaking tests. But there ist a difference between the particle size dependent curves when both examined materials are regarded. Due to heterogeneous composition ofthe material, consisting of several compounds as mortar,
290 250
12000-
Fig. 7
Fig. 8
200 0
E
P
z 0
150
:
Yu
100
50
0
I I I 2,O-0,8 0.8-0,4 0,4-0,l
I 6,3-2,0
>6
>6,3
2,O-0,8 0,8-0,4 0.4-0,lc O , ~
6,3-2,0
particle size (mm)
particle size (mm)
debris (HBS)
fly-ash-cement (FAZ)
r ..u..
A
0,0007
Fig.9
0,0006
:*. .... ,.,
0,0005-
......
-
.......-.
L,.
0,0002
i
0,0001
0,15 -
p...’”
N
-F
0
.......... 9...........
o,...
-c
.....a
...... ,L1..‘
0,l-
m
, ,+,
z
x-
,’.,..
r _ _ _ l , ’
>6,3
6,3-2,0 2,O-0,8 0,8-0,40,4-0,l<0,1
>6,3
2,O-0,8 0,8-0,40,4-0,l<0,1
6,3-2,0
particle size (mm) column-test
particle size (mm) column-test
fly-ash-cement (FAZ),
K
Na
Cr
...
0
- @ .
debris (HBS): K
Na
Cr
-c.
-c.
-L-
29 1
bricks or cement, a rather unsteady concentration curve of HBS leachates was expected. But a continuous increase of Cr, Na and K concentrations with decreasing particle size was detected. Opposite tothe HBS material, leaching of particle size fractions of the very homogeneous FAZ was resulting in Cr, Na and K concentration curves with a maximum in the 0 , 4 - 0 , 0 nun fraction. The same shape is visible from figures which show the dependence of CEC from particle size. By regarding our results avaiable up to now, this coincidence can be explained with the fact that the elements were in an exchangeable state before leaching out of the investigated materials. Change of CEC with particle size can be explained with the total surface area, whose curve show the same shape. Taking the value for the theoretic spherical surface as basis, an expotential increase of total surface can be expected. Leachate analyses of the HBS material were fulfilling these expectations. Decrease of total surfaces of particle size fractions 0 , 4 - 0 , 4 mm and < 0,lmm of FAZ can only be explained by chemical transformations ash is consisting to the on surfaces of the fine particles. Fly greater extend of small glazed globules which can be destroyd in the fine fractions. With that, new reactive surfaces were formed which lead to a agglutination of the filigree structure elements. In this way, the avaiable inner surfaces could have been reduced. Chemical transformations at particles surfaces are probable, because the particle size dependent pH values of this homogenous material are showing relatively strong variations. The strong variations of particle size dependent HBS leachate pH canbemost easily explainedwith inhomogenous distribution of material in the distinct particle size fractions. There seems to be less influence of the high pH values on the leaching behaviour of the examined materials. A coincidence ist only visible between pH and electric conductivity of the FAZ. The experiments are showing that there are no simple relations between particle size and leaching parameters. Even total surface is not automatically increasing with decreasing particle size. This phenomenon is even visible at a apparent homogenous and pore - free
-
292
material like basalt. Also, there can be a particle size dependent mobilization of the elements to be investigated. E.g. a liniear liberation of Sulfate with decreasing FAZ particle size or a maximum curve, describing the KandNa - c o n t e n t o f F A Z l e a c h a t e w a s detected. Other investigations, dealing with the particle size dependent leaching cf steel-works slag, lead to a miniumum curve for Vanadium and an increase of Chromium with decrease of particle size. But these experiments show that the total surface of the materials is often determining the leaching of elements. The surface to amount of element leached - ratio is nearly equal for all particle size fractions (Fig. 9,lO). This means under the aspects of practical uses, that grinding of sample material must not lead automatically to a increasedleaching. A convention for the particle sizes to be investigated is useful to assure a comparability of different materials.