Iraqi Journal of Chemical and Petroleum Engineering

Vol.12 No.3 (September 2011) 25-33

ISSN: 1997-4884

Aluminum Leachability Evaluation from Oven Dried Alum Sludge
Sami Mohammed Zaboon

University of Baghdad , College of Engineering ,Chemical Engineering Department,Baghdad, Iraq.

Abstract

Phosphorus and dye (direct black) removal for small – scale wastewater applications

were investigated using oven dried alum sludge (ODS).The use of alum sludge not

only provides a low cost technique but also reduces the hazard and the cost related to

the disposal of large amount of alum sludge. Phosphorus and dye removal exceeds

90% for all operating conditions applied in the research.

The residuals generated during the treatment of wastewater were further tested to

study the possibility of aluminum leaching from oven dried alum sludge during the

adsorption of phosphorus and dye. These tests observed a reduction in aluminum

leaching indicating a lower risk imposed on land and surface water based on disposal

options rather than on alum sludge disposal.

The leaching of aluminum was observed to be mostly below 1 mg/l for a pH

solution of 6 and 7 for both processes of phosphorus and dye removal. However, the

pH of 5 seemed to have a concentration of more than 1mg/l of aluminum.

Introduction
Biosolid management is considered

very important, as there are

considerable amounts of biosolids

generated due to anthropogenic

reasons. Alum sludge, a biosolid

generated in the coagulation process in

a water treatment plant, is one ofthem.

The reuse of alum sludge in other

applications has been considered by

many researchers in recent

years.Divalent and trivalent cation

based materials are known to be

effective for phosphorous and dyes

removal (Maruf, M., 2006,Sarmad, A.,

2009 and Rasha, H., 2010).

Alum sludge is typically known to be

a mixture of various forms of

aluminium hydroxide (Wang et al.,

1992). The use of waste material (alum

sludge) not only can provide low cost

appropriate technological alternative

for small – scale applications, but also

can reduce the hazard and the cost of

the disposal of large amount of alum

sludge.Physical and chemical methods

are considered very expensive in terms

of energy and reagent consumption.

Another account that limits their use is

the excessive sludge they generate

(Yokubuet al., 2008).Adsorption has

been found to be superior to other

techniques for water reuse in terms of

initial cost, simplicity of design, ease

of operation and insensitivity to toxic

substances.At the present time, there is

a growing interest in using low – cost,

commercially available materials for

the adsorption of phosphorous and

dyes.Sarmad(2009) investigated the

removal of phosphorous from

wastewater by using oven dried alum

sludge. The results showed that the

oven dried alum sludge were effective

for adsorbing phosphorous and the

removal percentage was up to 85%.

University of Baghdad

College of Engineering

Iraqi Journal of Chemical and

Petroleum Engineering

Aluminum Leachability Evaluation from Oven Dried Alum Sludge

26 IJCPE Vol.12 No.3 (September 2011) -Available online at: www.iasj.net

Rash H. (2010) investigated the

removal of dyes from wastewater by

using oven dried alum sludge. The

results showed that the removal was

92%.

Phosphorous and dyes adsorption

onto oven dried alum sludge shown in

the researches mentioned earlier

provided an environment friendly

management option for water

treatment residuals . However, the

residuals generated during the process

of adsorption on oven dried alum

sludge are also needed to be managed

due to large amount of aluminum in

these residuals and aluminum in water

has proven to produce chronic toxicity

(Allin and Wilson ,1999).

The chemical speciation of

aluminum in natural water regulates its

mobility, bioaviability and toxicity.

Aluminum normally undergoes

hydration reaction in aqueous system

to an extent governed by the ligand

properties and concentrations of

aluminum, and hydrogen ion (Faust

and Aly, 1999). Hydrolysis increases

as the solution pH increases resulting

in a series of aluminum hydroxide

complexes. Alum sludge is mostly

composed of these series of aluminum

hydroxide complexes (i.e. Al(OH)2
+
,

Al(OH)3, Al(OH)4, Al
+3

, … etc).

The objective of this study was to

study the leachability of residuals (i.e.

aluminum) generated from adsorption

of phosphorous and dyes from small –

scale wastewater on alum sludge.

 Materials
1. Adsorbent
 Alum Sludge
Alum sludge is a waste material

generated during the coagulation /

sedimentation process in a drinking
water treatment plant. Alum sludge that
is generated from drinking water
treatment contains precipitated alum
hydroxide and the contaminants that are
specific to row chemistry. In this research,

alum sludge was collected from Al-
Qadisiya treatment plant, Baghdad
governorate, Iraq. Inorganic materials in
alum sludge are presented in table 1.

Table 1, Inorganic materials in alum

sludge

The alum sludge used in this research

was heated in an oven at 105 C
o
for 24

hours. The dried sludge was then

cooled to room temperature. The

sludge particles were then crushed to

produce a particle size of 2.36 mm.

The physical properties are listed in

table 2.

Table 2, Physical properties of oven

dried alum sludge

2. Wastewater

 Orthophosphate(Potassium
Dihydrogen Orthophosphate

KH2PO4) was used in this study to

prepare a phosphorus solution.

Physical properties of KH2PO4 are

listed in table3.

Constituent
Weight
percent

Aluminum 3.38 %

Iron 0.819 %

Manganese 0.16 %

Chromium 0.013 %

Vanadium 0.002 %

Zinc 0.0098 %

Lead 0.0001 %

Barium 0.0001 %

Arsenic 0.0002 %

Item name
Oven dried alum

sludge

Bulk density (kg/m
3
) 786.7

Particle porosity 0.7

Bed porosity 0.65

Sami Mohammed Zaboon

-Available online at: www.iasj.net IJCPE Vol.12 No.3 (September 2011) 27

Table 3, Main properties of adsorbate

Name of
component

Potassium
dihydrogen

orthophosphate

Chemical symbol KH2PO4

Name of
company

The British Drug
Houses LTD /

England

Molecular
weight

136.09 kg / kg.mole

Assay
(acidimetric)

99 to 101per cent

Chloride (Cl)
Not more than 0.01

per cent

Sodium (Na)
Not more than 0.2

per cent

Sulphate (SO4)
Not more than 0.05

per cent

pH (1 percent
solution)

4.5 to 4.7

 Deionized water was spiked with
KH2PO4 to prepare a phosphorus

solution of (10) mg/L, this

concentration was achieved by

0.0143 mg KH2PO4 with liter of

water. The phosphorus

concentration was chosen as typical

phosphorus concentration in many

wastewaters. The same thing was

used to prepare the dyes solutions.

 Black direct dye of 10 mg/l was
used as adsorbate. The

concentration of dye was measured

with Shimatzu UV

Spectrophotometer at wave length

corresponding to the maximum

absorbance of 566nm.

 Experimental Arrangements

The schematic representation of

experimental equipment is shown in

Figure 1.

 Adsorption Column
The fixed bed adsorber studies were

carried out in Q.V.F. glass column of 2

in. (50.8 mm) I.D. and 50 cm

height.The oven dried alum sludge was

confined in the column by fine

stainless steel screen at the bottom and

a glass cylindrical packing at the top of

the bed to ensure a uniform

distribution of influent through the

alum sludge.The influent solution was

introduced to the column through

aperforated plate, fixed at the top of the

column.

Experiments were carried out at

various pH solutions (5 – 7) with

keeping other variables constant (i.e.

initial phosphorus and

dyeconcentration, particle size, flow

rate and bed depth).

The experimental procedure for

column system experiments is as

follow:

 The oven dried alum sludge with
particle size of 2.36 mm was

placed in the adsorption column

for the desired bed length (i.e. 40

cm)

 The wastewater with the desired
concentration was prepared in the

feed container, using distilled

water (i.e. phosphorusconc. 5 ppm

and dye conc. 10 ppm).

 The wastewater was pumped to
the adsorption column through the

calibrated rotameter at the desired

flow rate (i.e. 1.67 × 10
-6

m
3
/s).

 Samples were taken periodically,
the concentration of phosphorus,

dye, and aluminum in these samples

were measured using UV

spectrophotometer and atomic

absorption.

Aluminum Leachability Evaluation from Oven Dried Alum Sludge

28 IJCPE Vol.12 No.3 (September 2011) -Available online at: www.iasj.net

Fig. 1, Schematic representation of experimental equipment

 Tests for Characterizing Oven
Dried Alum Sludge

a. IR Spectroscopy

The samples for infrared spectra

(Bruker Vector FT-IR spectrometers)

were prepared with methylene chloride

(CH2Cl2) mulls onCsI plates.

Vibrational spectra were reported in

wavelengths (cm
-1

) against ranked

infrared absorption, where the value of

the wavelengths at peak corresponds to

the characteristics of the active groups

present on the surface of the material.

This test was done in the College of

Science / Chemistry Dept. and the

result is shown in Figure 2.

b. X-Ray Diffraction
X-Ray powder diffraction patterns of

ODS were obtained from gently

pressed specimens of random powder

particles that are less than 0.45 μm.

Powder X-ray diffraction data were

collected from 10 to 60° 2 with a

Nicolet X-ray powder diffractometer

(graphite monoachromatized Cu KR

radiation, 0.05° 2 step size, and 2-s

count time per steps).This test was

carried out in theMinistry of Science

and Technology and the result obtained

is shown in Figure 3.

c. Specific Surface Area
In practice, the method mostly used

for determining specific surface area is

To drain

Sampling

point

Centrifugal

pump

Feed

tank

Effluent

tank

Feed distributor

Rotameter

Sampling

point

To drain

Feed

Adsorber

Sami Mohammed Zaboon

-Available online at: www.iasj.net IJCPE Vol.12 No.3 (September 2011) 29

the BET method (Brunauer, Emmett

and Teller) based on the physical

adsorption of an inert gas at constant

temperature of liquid nitrogen. The

principle of measurement consists of

determining the point when molecular

layer of gas covers the surface

(Lepage, 1987).The apparatus of type

Carlo-Erabasorptomic series 1800 was

connected to computer in which

allenecessary BET principles were run

from the information of the pressure

decrease. This test was done in

Petroleum Research and Development

Center.

The experimental results showed that

oven dried alum Sludge had an average

specific surface area of 191 m
2
/g.

Fig. 2, IR Spectroscopy of ODS

Results and Discussion

To study the possibility of aluminum

contaminants leaching from oven dried

alum sludge,a series of experimental

breakthrough curves were carried out

for adsorption of phosphorus and dyes

using oven dried alum sludge. The

experiments includedstudying the

effect of pH solution (5, 6, and 7) on

phosphorus and dyes adsorption onto

oven dried alum sludge and aluminum

leaching from the adsorbent.

Fig. 3, X-Ray Diffraction of ODS

 Phosphorus Adsorption:
The removal of phosphorus by using

oven dried alum sludge, as a function

of different values of pH is presented

in Figures4, 6, and 8. Varied values of

pH solution are 5, 6 and 7. The other

variables (phosphorus concentration 5

ppm, operating temp. 25C, bed height

40 cm, particle size 2.36 mm) are kept

constants.

The results indicate that pH had little

effect on the adsorption density.

However, pH

solution of 6 appeared to produce

maximum phosphorus adsorption

density.

In the same time, tests conducted on

oven dried alum sludge showed lower

tendency to leach aluminum.

Aluminum leaching was in general

high in the beginning of the

experiments as shown in Figures 5, 7,

and 9. However, over time, aluminum

leaching decreased. In many cases,

aluminum concentrations were lower

than the concentration present in the

raw water because of the structural

variation in alum sludge surfaces

during the drying process. Also, the pH

of the system affects both metal ion

and waste water solution. The solution

Aluminum Leachability Evaluation from Oven Dried Alum Sludge

30 IJCPE Vol.12 No.3 (September 2011) -Available online at: www.iasj.net

suffers protonation as the pH of the

system decreases:

If the solution is unable to ionize as a

result of the concentration of hydrogen

ion, it will not be able to form a

complex with a metal ion, and hence

extraction will not occur.

The effluent pH was understandably

dependent on the influent pH. An

influent pH 5 produced effluent pH of

(4.7-5.5). Similarly an influent pH 6

generated an effluent pH range (5.6-

6.3) and an influent pH 7 generated an

effluent pH range of (6.5-7.5). This

was due to the adsorption and

desorption of H
+
ions during the

adsorption of phosphorus on alum

sludge. An effluent pH below 4.5 is

not suitable for disposal in surface

water. The effluent pH can be

increased prior to disposal in surface

water. However, the cost of chemicals

to reduce initial pH and to increase

final pH and hazards of dealing with

increased amount of sludge would pose

negative interest for pH control.

In general, a pH value in the range of

6 – 9 is reasonable for wastewaters

before disposal into surface water.

Fig. 4, Phosphorus ratio (C/Co)

concentration with time

Operating Conditions:Phosphorous conc. =

5ppm, operating temperature=25⁰C, bed height
= 40cm, column diameter= 2in., particle size =

2.36 mm, pH=5, Q=1.67×10
-6

m
3
/s.

Fig. 5, Aluminum concentration

with time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in., particle

size = 2.36 mm, pH=5, Q=1.67×10
-6

m
3
/s.

Fig. 6, Phosphorus ratio (C/Co)

concentration with time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in.,particle
size = 2.36 mm, pH=6, Q=1.67×10

-6
m

3
/s.

0.2

0.4

0.6

0.8

0 5000 10000 15000 20000 25000 30000

P
h

o
s
p

h
o

r
o

u
s
C

o
n

c
.
C

/
C

Time, sec

0.0

0.4

0.8

1.2

1.6

2.0

0 5000 10000 15000 20000 25000 30000

A
lu

m
in

u
m

C
o

n
c
.
m

g
/
l

Time, sec

0.2

0.4

0.6

0.8

0 5000 10000 15000 20000 25000 30000

P
h

o
s
p

h
o

r
o

u
s
C

o
n

c
.
C

/
C

Time, sec

H
+

-H
+

H
+

-H
+

HA
+
A

¯
H2A

Sami Mohammed Zaboon

-Available online at: www.iasj.net IJCPE Vol.12 No.3 (September 2011) 31

Fig.7, Aluminum concentration with

time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in., particle

size = 2.36 mm, pH=6, Q=1.67×10
-6

m
3
/s.

 Direct Black Dye Adsorption
The removal of direct black dye by

using oven dried alum sludge, as a

function of different values of pH is

presented in Figures 10, 12, and 14.

Varied values of pH are 5, 6, and 7.

The other variables (dye concentration

10 ppm, operating temperature 25
o
C,

bedheight 40 cm, particle size 2.36

mm)are kept constants.

The effluent pH levels were in the

range of 5.5 – 7.5 for an is influent pH

of 5 – 7 and this mostly suitable for

disposal in surface water.The results

showed that the oven dried alum

sludge was effective in adsorbing dyes

with removed efficiency up to 93%.

Aluminum leaching was in general

about 1 mg/l in the beginning of the

experiments for each pH a shown in

the Figures 11, 13, and 15. However,

over time, aluminum leaching

decreased to less than 0.2 mg/l; this

was due to the structural variation in

alum sludge surfaces during drying

process and the effect of pH solution

that discussed previously.

Fig. 8, Phosphorus ratio (C/Co)

concentration with time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in., particle

size = 2.36 mm, pH=7, Q=1.67×10
-6

m
3
/s.

Fig.9, Aluminum concentration with

time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in., particle

size = 2.36 mm, pH=7, Q=1.67×10
-6

m
3
/s.

Fig.10, Direct black dye

concentration with time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed

0.0

0.4

0.8

1.2

1.6

2.0

0 5000 10000 15000 20000 25000 30000

A
lu

m
in

u
m

C
o

n
c
.,

m
g

/
l

0.2

0.4

0.6

0.8

0 5000 10000 15000 20000 25000 30000

P
h

o
s
p

h
o

r
o

u
s
C

o
n

c
.
C

/
C

Time, sec

0.0

0.4

0.8

1.2

1.6

2.0

0 5000 10000 15000 20000 25000 30000

A
lu

m
in

u
m

C
o

n
c
.,

m
g

/
l

Time, sec

0.2

0.4

0.6

0.8

0 5000 10000 15000 20000 25000 30000

D
y

o
n

c
.
C

/
C

Time, sec

Aluminum Leachability Evaluation from Oven Dried Alum Sludge

32 IJCPE Vol.12 No.3 (September 2011) -Available online at: www.iasj.net

height = 40cm, column diameter= 2in.,
particle size = 2.36 mm, pH=5, Q=1.67×10

-6

m
3
/s.

Fig.11, Aluminum concentration

with time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in., particle

size = 2.36 mm, pH=5, Q=1.67×10
-6

m
3
/s.

Fig.12, Direct black dye

concentration with time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in., particle

size = 2.36 mm, pH=6, Q=1.67×10
-6

m
3
/s.

Fig.13, Aluminum concentration

with time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in.,
particle size = 2.36 mm, pH=6, Q=1.67×10

-6

m
3
/s.

Fig.14, Direct black dye

concentration with time
Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in., particle

size = 2.36 mm, pH=7, Q=1.67×10
-6

m
3
/s.

Fig.15, Aluminum concentration

with time

0.0

0.4

0.8

1.2

1.6

2.0

0 5000 10000 15000 20000 25000 30000

A
lu

m
in

u
m

C
o

n
c
.
m

g
/
l

Time, sec

0.2

0.4

0.6

0.8

0 5000 10000 15000 20000 25000 30000

D
y

o
n

c
.
C

/
C

Time, sec

0.0

0.4

0.8

1.2

1.6

2.0

0 5000 10000 15000 20000 25000 30000

A
lu

m
in

u
m

C
o

n
c
.,

m
g

/
l

Time, sec

0.2

0.4

0.6

0.8

0 5000 10000 15000 20000 25000 30000

D
y

o
n

c
.
C

/
C

Time, sec

0.0

0.4

0.8

1.2

1.6

2.0

0 5000 10000 15000 20000 25000 30000

A
lu

m
in

u
m

C
o

n
c
.,

m
g

/
l

Sami Mohammed Zaboon

-Available online at: www.iasj.net IJCPE Vol.12 No.3 (September 2011) 33

Operating Conditions: Phosphorous conc. =

5ppm, operating temperature= 25⁰C, bed
height = 40cm, column diameter= 2in., particle

size = 2.36 mm, pH=7, Q=1.67×10
-6

m
3
/s.

Conclusion

 Oven dried alum sludge was
effective in adsorbing phosphorus

and direct black dye.

 Experimental findings indicated the

residuals generated during

adsorption of phosphorus and dye

on oven dried alum sludge would

not cause alarming level of

aluminum leaching. Therefore,

there were low chances of these

residuals being a problem for

disposal.

References

 MarufMortula, Meaghan Gibbons,
and A. Gagnon, 2006,

"Phosphorus Adsorption by

Naturally-Occurring Materials and

Industrial by-Products", J.

Environ. Eng. Sci., 6, pp 157-164.

 Yakubu, M.K., Gumel M.S., and
Abdullahi A.M., 2008, "Use of

activated carbon from date seeds

to treat textile and tannery

effluents", African Journal of

science and technology (AJST),

Science and Eng. Series, 9(1), p.

39 – 49.

 Sarmad, A.R., 2009, "Phosphorus
Removal from Wastewater Using

Alum", M. Sc. Thesis, University of

Baghdad.

 Wang, M.C., Hull, J.Q., Jao, M.,
Dempsey, B.A., and Cornwell,

D.A., 1992,"Engineering behavior

of water treatment sludge", Journal

of Environmental Engineering,

118 (6), 848 – 864.

 Rasha H. Salman, 2010,"Removal

of Dyes from Textile Effluent by

Adsorption onto Oven Dried Alum

Sludge", Journal of Engineering,

No.2, 16 (5249 – 5262).

 Allin, C.J., and Wilson, R.W.,
1999,"Behavioral and Metabolic

Effects of Chronic Exposure to

Sublethal Aluminum in Acidic

Soft Water in Juvenile rainbow

trout", Canadian Journal of

Fisheries and Aquatic Science, 56

(670 – 678).

 Faust, S.D., and Aly, O.M., 1999,
"Chemistry of Water Treatment",

2
nd

edition, Lewis Publishers.