Iraqi Journal of Chemical and Petroleum Engineering 

 Vol.15 No.3 (September 2014) 9-18 

ISSN: 1997-4884 

 
 
 
 

Corrosion Inhibition of Mild Steel by Curcuma Extract in Petroleum 

Refinery Wastewater 

  
Aprael S. Yaro

a
 and Kabas F. Talib

 b
 

Chemical Engineering Department-College of Engineering- University of Baghdad, Iraq 
a, E-mail: Apraely@yahoo.com      

b, E-mail: barby_eng_1990@yahoo.com 

 
Abstract 

   The inhibitor property of curcuma longa L. extract in different concentrations of 

simulated refinery wastewater (0.05% - 2% wt) and at various temperatures (30, 35 

and 40 ˚C) was investigated using weight loss method. The results showed that the 

presence of about 1.2 % (v/v) of curcuma extract gave about 84% inhibition 

indicating its effectiveness on mild steel corrosion in simulated refinery wastewater, 

besides the adsorption process on the mild steal surface obeyed the Langmuir 

adsorption isotherm. 

 
Keywords: Corrosion, oil industry, Steel, Curcuma extract 

 

Introduction 

   Mild steel is one of the most widely 

used engineering materials, despite its 

relatively limited corrosion resistance. 

Corrosion is one of the main concerns 

in the durability of metallic materials 

and their structures. Many efforts have 

been made to develop a corrosion 

inhibition process to prolong the life of 

existing structures and minimize 

corrosion damages [1]. 

Water pollution not only is 

harmful to mankind but also is harmful 

to metallic equipment such as 

pipelines, storage tanks, pumps, heat 

exchangers, etc., that are used in 

handling wastewater [2]. In addition to 

causing the eventual failure of the 

metallic equipment, corrosion by 

industrial wastewater leads to water 

pollution by the dissolved metal ions 

such as Cu
++

, Cd
++

 and Pb
++

, which 

themselves also may be toxic [3]. The 

type and rate of corrosion depends on 

the nature and concentration of 

pollutants present in the wastewater. 

Steel suffers severe corrosion attack in 

wastewater containing electrolytes. 

The rate of corrosion depends, amongst 

other factors, upon the concentration of 

oxygen and the motion of water. Steel 

with residual stresses undergoes stress 

corrosion cracking in wastewater 

containing nitrates, for example in the 

case of agricultural runoff waters 

containing nitrate fertilizer. Mild steel 

sustains severe damage in wastewater 

solutions containing chlorides, where 

pitting corrosion and stress corrosion 

cracking take place [4, 5]. 

   Crude oil usually contains some 

water-dissolved salts such as CaCl2 

and MgCl2. Before processing crude 

oil in the distillation tower, the water 

Iraqi Journal of Chemical and 
Petroleum Engineering 

 

University of Baghdad 
College of Engineering 

mailto:eng_1990@yahoo.com


Corrosion Inhibition of Mild Steel by Curcuma Extract in Petroleum Refinery Wastewater 
 

10                                   IJCPE Vol.15 No.3 (September 2014)          -Available online at: www.iasj.net 
 

should be removed first by a process 

known as dehydration and desalting. 

Early water removal from crude oil 

minimizes corrosion of process 

equipment such as pumps, heat 

exchangers, distillation towers and 

condensers. On the other hand, the 

equipment used for handling water that 

has been separated from the oil can 

suffer from severe corrosion, 

depending upon the salt content of 

water
 
[6]. 

A wide range of materials known as 

inhibitors are used to control the 

corrosion. The recent trend is towards 

developing environment friendly 

inhibitors. Most of the natural products 

are non-toxic, bio-degradable and 

readily available in plenty. Various 

parts of plants-seeds, fruits, leaves, 

flowers, etc. have been used as 

corrosion inhibitors [7]. The present 

work is another trial to find the effect 

of aqueous extract of the plant material 

known as Curcuma powder as a green 

inhibitor for mild steel in petroleum 

refinery wastewater produced from 

desalting process of crude oil. 
 

Experimental Work 

   Synthetic magnesium chloride 
solution, simulated refinery 

wastewater, produced from desalting 

process of crude oil [8] were used, 

under static conditions in the presence 

and absence of curcuma extract  as a 

corrosion inhibitor of concentrations of 

1, 5 and 9 ml/250ml of MgCl2 solution 

which was used as corrosive media at 

30 ˚C. The corrosion rate of mild steel 

was found by weight loss method. 
 

Materials 

   A mild steel sheet (supplied by 

engineering Lab. and Inspection 

department, Ministry of Science and 

Technology) was used as working 

electrode with the following chemical 

composition: 

 

Table 1: The chemical composition of mild 

steel coupon (wt %) 

wt% Component 

0.069 Carbon 

0.441 manganese 

0.026 Nickel 

0.005 sulfur 

0.009 silicon 

Remainder Fe 

 

Test specimens of rectangular shape 

with 1.5 cm (width), 3.5 cm (length) 

and 0.1 cm thickness were used in 

weight loss method.  

 

Solutions 

 Simulated petroleum refinery 
wastewater: The wastewater was 

prepared by dissolving appropriate 

amount of MgCl2 in one liter of 

distilled water. 

 Aqueous extract of Curcumin dye: 
   10 g of rhizome (Curcuma longa L.) 

powder was weighed and boiled with 

double distilled water. The yellow dye 

curcumin was filtered to remove 

suspending impurities and made up 

to100 ml. The curcumin dye (CD) was 

used as corrosion inhibitor in the 

present study [9]. 
 

Weight loss Method 

A. Specimen Preparation: 
Coupon specimens were annealed in 

a vacuum at 600 ˚C for 1.0 h and 

the furnace was cooled to room 

temperature. This was carried out in 

order to remove mechanical 

stresses. An annealed specimens 

were  abraded  in sequence under  

running tap water using emery 

paper of grade 120, 220, 320,400 

and 600, respectively ,washed  with  

running tap water followed by 

distilled water ,dried on clean tissue, 

immersed in benzene for 5 seconds  

and dried with clean tissue 

,immersed  in acetone for 5 seconds  

and dried with clean tissue and then 



Aprael S. Yaro and Kabas F. Talib  

 

-Available online at: www.iasj.net                   IJCPE Vol.15 No.3 (September 2014)                          11 
 

kept in desiccators  over silica gel  

until use. 

 

B. Procedure: 
1. The dimensions of each specimen 

were measured with Vernier to the 

2
nd

 decimal of millimeter and 

weighed accurately to the 4
th

 

decimal of gram before using. 

2. Specimens were completely 
immersed in 250 ml of corroding 

solution contained in (500 ml) 

beakers. They were exposed for 

period of 24 h, at required 

temperature, desired concentration 

of inhibitor and required 

concentration of solutions.  

After each test, the specimen was 

washed with running tap water, 

scrubbed with a brush to remove 

corrosion products, washed with tap 

water followed by distilled water and 

dried on a clean tissue, immersed in 

benzene, dried, immersed in acetone, 

dried and left in a desiccators over 

silica gel for one hour before 

weighting.  
 

Results and Discussion 

   A total of 18 runs for weight loss 
measurements were made expressing 

the corrosion rate of mild steel in 

simulated petroleum refinery 

wastewater with an increasing 

concentration from 0.05 to 2% wt. The 

parameters studied were concentration 

of MgCl2 and concentration of 

corrosion inhibitor (aqueous extract of 

Curcuma). 

  Corrosion rate calculations from 

weight loss data were performed 

according to Eq. 1: 
 

   
              

                     
             …(1) 

 
The results showed in Tables 2 and 3 

express the corrosion rate and 

inhibition efficiency of mild steel in 

simulated petroleum refinery 

wastewater with different 

concentrations of aqueous extract of 

Curcuma as green inhibitor. 
 

Table 2: Corrosion Rate (gmd) of mild steel in 

simulated petroleum refinery wastewater with 

different concentration of extracted Curcuma 
at 30 ˚C 

Curcuma     

(ml/250 

ml soln.) 

MgCl2 wt% 

0.05 1.025 2 

0 4.9263 4.4162 4.0235 

1 2.8959 2.7220 3.4620 

3 0.7761 2.0883 3.1772 

5 0.9939 1.5426 2.6560 

7 1.2715 1.4540 2.0344 

9 1.7013 1.6263 2.2035 

 

Table 3: Inhibition Efficiency (IE %) of 

different concentrations of extracted Curcuma 

in simulated petroleum refinery wastewater at 

30 ˚C 

Curcuma 

(ml/250ml 

soln.) 

MgCl2 wt% 

0.05 1.025 2 

1 41.21 38.36 13.96 

3 84.25 52.71 21.03 

5 79.83 65.07 33.99 

7 74.19 67.08 49.44 

9 65.47 63.17 45.24 

 

 
Fig. 1: Corrosion rate and inhibition efficiency 

of mild steel as function of inhibitor 

concentrations (extracted Curcuma 

concentration) in simulated petroleum refinery 

wastewater at 30
 
˚C 

 

The results showed in Tables 2 and 3 

and Figure 1 indicate that the addition 

of aqueous extract of Curcuma as 

corrosion inhibitor to different 

concentrations of simulated petroleum 



Corrosion Inhibition of Mild Steel by Curcuma Extract in Petroleum Refinery Wastewater 
 

12                                   IJCPE Vol.15 No.3 (September 2014)          -Available online at: www.iasj.net 
 

refinery wastewater decreased the 

corrosion rate of mild steel. (ie., the 

maximum corrosion inhibition 

achieved was 84.25% and the 

minimum one was 13.96%). 

   Regression analysis was utilized by 

using STATISTICA program version 

10.1 to generate a model to describe 

the response of the mild steel with 

correlation coefficient of R
2
=0.91 

through implementing the 2
nd

 order 

polynomial model. 

 

CR (gmd) = 4.005950 -0.164999X1 -

0.914977X2+0.190011X1
2
+0.067442X

2
2
+0.053740X1X2                         …(2) 

 

Where X₁ and X₂ are MgCl2 
concentration, and inhibitor 

concentration, respectively. 

   Equation 2 is applied to estimate the 

corrosion rate of the mild steel in 

simulated petroleum refinery 

wastewater. 

   The quantitative description of the 

physical condition effect on corrosion 

rate of mild steel in simulated 

petroleum refinery wastewater 

performed. An empirical modeling 

technique called response surface 

methodology is used to evaluate the 

relationship between the controllable 

experimental variables and observed 

results [10]. Figures 2 and 3 show the 

effect of studied variables on the 

corrosion rate and inhibition of mild 

steel in refinery wastewater, 

respectively. 

   Figure 2 corroborates that the 

minimization of corrosion rate of mild 

steel is possible in refinery wastewater 

containing low concentration of 

MgCl2% and high concentration of 

extracted Curcuma. The darker the red 

color means higher corrosion rate, 

while the darker the green color means 

the lowest one. 

   Figure 3 shows the response surface 

for the inhibition of mild steel due to 

the effect of MgCl2% concentration 

and Curcuma extract concentration. 

The darker the red color means the 

higher the inhibition efficiency, while 

the darkest the green one means the 

lower the inhibition efficiency. 

 

 

 > 4 

 < 4 

 < 3 

 < 2 

 < 1 

0

1
2

3
4

5
6

7
8

9

Ex
tra

cte
d C

urc
um

a (
ml

/25
0m

l s
oln

.)

0.0
0.

2
0.4

0.
6

0.
8

1.0
1.

2
1.

4
1.6

1 .
8

2 .
0

M
gCl2 wt%

1

2

3

4

5

C
R

 (g
m

d
)

 
Fig. 2: Corrosion rate response surface for MgCl2 concentration and extracted Curcuma 

 



Aprael S. Yaro and Kabas F. Talib  

 

-Available online at: www.iasj.net                   IJCPE Vol.15 No.3 (September 2014)                          13 
 

 

 

 > 80 

 < 64 

 < 44 

 < 24 

 < 4 

0
1

2
3

4
5

6
7

8
9

Ex
tra

cte
d C

urc
um

a (
ml

/25
0m

l s
oln

.)

0.0
0.2

0.
4

0.
6

0.8
1.

0
1 .

2
1 .4

1 .
6

1 .8
2 .

0

M
gCl2 wt%

20

40

60

80

100

In
h
ib

itio
n
 E

ffe
ic

ie
n
c
y

 
Fig. 3: Inhibition efficiency response surface for MgCl2 concentration and extracted Curcuma 

 
Adsorption Studies and Inhibition 

Mechanism 
   The primary step in the action of 

inhibitors in MgCl2 solution is 

generally agreed to be adsorption on 

the metal surface. This involves the 

assumption that the corrosion reactions 

are prevented from occurring over the 

area (or active sites) of the metal 

surface covered by adsorbed inhibitor 

species, whereas these corrosion 

reactions occurred normally on the 

inhibitor-free area [11]. Accordingly, 

the fraction of surface covered with 

inhibitor species    
   

   
  can be 

taken as a function of inhibitor 

concentration and solution 

temperature. The surface coverage (θ) 

data are very useful while discussing 

the adsorption characteristics. When 

the fraction of surface covered is 

determined as a function of 

concentration at constant temperature, 

adsorption isotherm could be evaluated 

at equilibrium condition. The 

dependence of the fraction of the 

surface covered θ on the concentration 

C of the inhibitor was tested 

graphically by fitting it to Langmuir’s 

isotherm, which assumes that the solid 

surface contains a fixed number of 

adsorption sites and each site holds one 

adsorbed species. Fig. 4 shows the 

linear plots for C/ θ versus C with R
2 

= 

0.97 as correlation coefficient, 

suggesting that the adsorption obeys 

the Langmuir’s isotherm: 

 
C/ θ =1/K +C                                …(3) 

 
Where C is the equilibrium inhibitor 

concentration, K adsorption 

equilibrium constant, representing the 

degree of adsorption (i.e. the higher the 

value of K indicates that the inhibitor 

is strongly adsorbed on the metal 

surface), the average value of K was 

2.25 l/g which was obtained as the 

reciprocal of intercept of Langmuir 

line, and the slop of this line is nearly 

0.5 meaning that each inhibitor 

molecule occupies half active site on 

the metal surface. 

 



Corrosion Inhibition of Mild Steel by Curcuma Extract in Petroleum Refinery Wastewater 
 

14                                   IJCPE Vol.15 No.3 (September 2014)          -Available online at: www.iasj.net 
 

 
Fig. 4: Longmuir adsorption isotherm for extracted Curcuma on mild steel 

 

Table 4: A Longmuir adsorption isotherm for 
curcuma extract on mild steel 

Inhibitor  

Conc. (C) 

ml/l 

MgCl2  

soln. 

C/ θ 

for 

0.05%  

MgCl2 

C/ θ 

for 

1.025%  

MgCl2 

C/ θ 

for 2% 

MgCl2 

1 9.71 10.43 28.65 

3 14.24 22.77 57.06 

5 25.05 30.74 58.84 

7 37.74 41.74 56.63 

9 54.99 56.99 79.58 
 

The Effect of Temperature 

   An attempt was made to find the 

effect of temperature on the corrosion 

rate of mild steel in refinery waste 

water. Table 5 shows the corrosion rate 

of mild steel in different concentrations 

of wastewater at different 

temperatures. 

 
Table 5: Corrosion rate of mild steel in 

different concentrations of wastewater at 

different temperatures 

MgCl2 

(wt%) 

Temperature 

25 

°C 

30 

°C 

35 

°C 

40 

°C 

E(cal/g

mol) 

0.05 3.06 4.93 5.16 5.56 6855 

1.025 2.92 4.42 4.58 5.46 7133 

2 2.78 4.02 4.35 5.43 7765 

 
The activation energy was calculated 

by plotting log C.R versus 1/T from 

the Arrhenius equation 

C.R = A exp (-E/RT)                 …(4) 
 
Where A = constant, R= gas constant, 

E=activation energy and 

T=temperature in K. 

 
   As shown in Figure 5, the rate of 

mild steel corrosion increased with 

increasing solution temperature, and 

the activation energy obtained was 

7.76 kcal/mol. The small value of the 

activation energy (7.76 kcal/mol) 

shows that the corrosion of mild steel 

in MgCl2 solutions is a diffusion-

controlled process [12]; i.e. the rate of 

mild steel corrosion is controlled by 

the diffusion of O2 from the solution 

bulk to the metal surface (Figure 6). 

This was consistent with previous 

studies [13, 14, 15], which reported 

that the corrosion of steel in the pH 

range 4-10 is controlled by the rate of 

diffusion of dissolved O2 from the 

solution bulk to the metal surface. 

Increasing the solution temperature 

increases the rate of corrosion (Figure 

7), primarily as a result of increased 

reaction kinetics, perhaps assisted by a 

reduction in the viscosity of the 

solution, with a consequent increase in 

the O2 diffusivity, according to the 

Stokes-Einstein equation [16]: 

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40

0.05 wt% MgCl2

1.025 wt%
MgCl2

2 wt% MgCl2



Aprael S. Yaro and Kabas F. Talib  

 

-Available online at: www.iasj.net                   IJCPE Vol.15 No.3 (September 2014)                          15 
 

Dµ/T = constant                            …(5) 
 

   Where D=diffusion coefficient and 

µ= solution viscosity. 
 

   In view of this, all effects that tend to 

increase the rate of transfer of 

dissolved oxygen from the solution to 

the metal surface, such as stirring, 

vibration, solution flow, etc. tend to 

increase the rate of corrosion. 

 

 

 
Fig. 5: Arrhenius plot of the experimental results at different MgCl2 concentration 

 

 

 

 
Fig. 6: Diffusion layer through which O2 diffuse from the solution bulk to the steel surface [12] 

   

y = -3450.3x + 12.815 

y = -3590.1x + 13.199 

y = -3908x + 14.19 

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

0.003180 0.003230 0.003280 0.003330 0.003380

0.05 wt%MgCl2

1.025 wt% MgCl2

2 wt% MgCl2

ln C.R 

1/T (k-1) 



Corrosion Inhibition of Mild Steel by Curcuma Extract in Petroleum Refinery Wastewater 
 

16                                   IJCPE Vol.15 No.3 (September 2014)          -Available online at: www.iasj.net 
 

 
Fig. 7: Effect of concentration of MgCl2 on the rate of corrosion at different temperatures 

 

The Effect of Temperature in 

Presence of the Inhibitor 

   An attempt was made to find the 

effect of temperature on the corrosion 

rate of mild steel in refinery 

wastewater in presence of the inhibitor. 

Table 6 shows the corrosion rate of 

mild steel in different concentrations of 

wastewater at different temperatures 

with the maximum concentration of the 

extracted curcuma 9 ml/250ml MgCl2 

solution.  

The activation energy was calculated 

by plotting log C.R versus 1/T from 

the Arrhenius equation. As shown in 

Figure 8, the rate of mild steel 

corrosion increased with increasing 

solution temperature, and activation 

energy obtained was 5 kcal/mol. 

   The inhibition efficiency of the 

maximum concentration of the 

extracted Curcuma (9 ml/250ml MgCl2 

solution) with different concentrations 

of MgCl2 solution at different 

temperatures is presented in Table 7. 

 

 
Fig. 8: Arrhenius plot of the experimental results at different MgCl2 concentrations with existing of 

extracted curcuma 9 ml/250ml MgCl2 soln 

2.0

3.0

4.0

5.0

6.0

0 0.5 1 1.5 2 2.5

25 c

30 c

35 c

40 c

MgCl2 concentration (wt%) 

C.R 

(gmd) 

y = -2537.5x + 8.7351 

y = -2539.9x + 8.8482 

y = -2675.6x + 9.6241 

0

0.2

0.4

0.6

0.8

1

1.2

0.00318 0.0032 0.00322 0.00324 0.00326 0.00328 0.0033 0.00332

0.05 wt% MgCl2

1.025 wt% MgCl2

2 wt% MgCl2

1/T (k-1) 

ln C.R 
 



Aprael S. Yaro and Kabas F. Talib  

 

-Available online at: www.iasj.net                   IJCPE Vol.15 No.3 (September 2014)                          17 
 

Table 6: Corrosion rate of mild steel in 

different concentrations of wastewater at 

different temperatures with extracted curcuma 

9 ml/250ml MgCl2 solution 

MgCl2 

(wt%) 

Temperature 

30 °C 35 °C 40 °C 
E(cal/

gmol) 

0.05 4.9263 5.1556 5.5556 5042 

1.025 4.4162 4.5828 5.4577 5046 

2 4.0235 4.3538 5.4255 5316 

 

Table 7: Inhibition efficiency of the optimum 

concentration of extract curcuma (9 cc/250ml 

MgCl2soln.) at different temperatures 

MgCl2 wt% 
Temperature 

30 
°
C 35 

°
C 40 

°
C 

0.05 70.65 68.66 65.98 

1.025 63.17 61.8 61.02 

2 45.24 40.95 45.16 

 

Conclusions 

1. The green corrosion inhibitor made 
up by the Curcuma extract 

successfully reduced the corrosion 

rates of mild steel in simulated 

refinery wastewater. 

2. In presence of Curcuma extract, the 
inhibition efficiency values 

generally increased with the 

inhibitor concentration, but 

decreased with rise in MgCl2 %wt 

at constant temperature. It is 

suggested that the absorption 

process was more favored at lower 

MgCl2% concentration.  

3. The Langmuir adsorption isotherm 
provided a formal description of the 

adsorptive behavior of the curcuma 

extract on mild steel surface. The 

values of Kads. indicated that 

inhibitor molecules occupied 

effective sites on the metal surface. 
 

References 

1- B. Bavarian, L. Reiner, “Corrosion 
Protection of Steel Rebar in 

Concrete with Optimal Application 

of Migrating Corrosion Inhibitors”, 

MCI 2022, 2–3, (2003). 

URL:www.cortecvci.com/Publicati

ons/Papers/mci_bavarian.pdf. 

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(1987). 

3- Salvato, J.A., “Environmental 
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Interscience, 3rd ed., Wiley, New 

York (1982). 

4- Fontana, M.G., “Corrosion 
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Corrosion Inhibition of Mild Steel by Curcuma Extract in Petroleum Refinery Wastewater 
 

18                                   IJCPE Vol.15 No.3 (September 2014)          -Available online at: www.iasj.net 
 

14- Jones, D.A., “Principles and 
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Macmillan, New York (1992). 

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