Fig. 6:Variation of charge vs. potential of

plated electrodes and pure electrodes

1.85

1.9

1.95

2

2.05

2.1

2.15

2.2

2.25

0 0.1 0.2 0.3 0.4

Aver

age

Pla

ting R

ate

of

copper

x10

-5

( g/c

m2.h

r)

Concentration of HCOH (mol/dm3)

Fig. 4: Variation of the average plating rate with

the formaldehyde concentration for Al substrate

ABSTRACT. A cathode material was developed in order to remove nitrates from landfill leachate

electrochemically by plating Cu on Al and mild steel substrates. An EDTA plating

bath was used for electroless deposition of Cu on the substrate material. The varied

HCOH concentrations in the plating bath resulted in a successful coating of Cu on

the Al substrate only. The developed Al electrodes were subjected to

characterization tests. It was found that higher concentrations of HCOH increased

the electroless plating rate and also resulted in the formation of smaller grains on

the Cu deposit which was confirmed by SEM images. The developed cathodes

were coupled with a Ti anode and employed to denitrify a synthetic leachate

sample. A percentage nitrate removal greater than 98% was achieved by all the

plated Cu cathodes compared to 74% achieved by a pure Cu cathode. However, a

significant difference in percentage nitrate removal was not observed among

developed cathodes.

METHODAluminum and steel sheets were shaped into electrodes of 1 cm X 1cm to be prepared for

electroless plating. Electrodes were plated using a plating bath of 0.11M EDTA, 0.05M

CuSO4 & NaOH. 0.1M, 0.2M and 0.3M formaldehyde solutions of varied concentrations were

used as the reducing agent in electroless plating of both substrates. Plating was carried at room

temperature as shown in Fig.2. Plated electrodes were characterized using cyclic voltammetry

(CV) and morphological analysis. Ti electrode was used as the counter electrode and saturated

calomel electrode was used as the Reference electrode in CV . Under morphological analysis

the electrodes were examined using a scanning electron micro-scope (SEM) and the surface

composition was detected using Energy Dispersive X-ray (EDX) analyzer. Then the developed

electrodes were used to denitrify synthetic leachate sample (shown in Fig.3) and the nitrate

removal percentage was determined by measuring nitrate concentration before and after

denitrification using spectrophotometry method. Aforementioned characterizations and

denitrification was done using a pure Cu electrode as a comparison

DEVELOPMENT OF CATHODE MATERIAL FOR ELECTROCHEMICAL DENITRIFICATION OF LANDFILL LEACHATE

S.T. Kariyawasm, M.K.D.C.S. Meegoda, Dr. K.G.N NanayakkaraDepartment of Civil Engineering, University of Peradeniya

INTRODUCTIONMajority of the solid waste produced ultimately end up in dumpsites. Leachate produced by

such dumpsites contain high levels of NO3-, which contaminates water and soil and could

cause diseases to humans. Thus nitrates in leachate have to be treated before disposal.

Treatment of nitrates using electrochemical methods is efficient and cost effective.

Efficiency of electrochemical methods could be amplified further by developing new

electrode materials. This study focused on developing a cathode using a low cost substrate

material by electroless deposition of Cu.

At the cathode surface NO3- reduces to nitrogen gas which is a harmless product but

ammonia and nitrite is also formed as intermediate products. Nitrites formed are further

reduced to N2 at the cathode as expressed by the equations below.

NO3- +3H2O+5e-→ ½ N2 +6OH-

NO3- +H2O+2e- → NO2

- +2OH-

NO2- +2H2O+3e- → ½ N2 +4OH-

NO3- +6H2O+8e- → NH3 +9OH-

The developed cathodes were characterized using scanning electron microscope and EDX in

order to study the surface morphology and composition respectively. The active surface area

was compared by cyclic voltammetric analysis. The denitrification process was conducted on

a synthetic leachate sample to investigate the percentage nitrate removal of each developed

cathode.

CONCLUSIONS

In this study it was identified that the electroless Cu deposition rate on Al increases with the

HCOH concentration. SEM images confirmed that higher concentrations of HCOH results in

the formation of smaller grains of deposited Cu up to 2µm in diameter. This agrees with the

SEM images obtained by Sha et al. (2011).

Cyclicvoltammograms revealed that surface charge on pure Cu electrode is much higher than

that on the developed Al electrodes. This indicates that the pure Cu electrode has a much higher

active surface area than the developed electrodes which directly contradicts with the findings of

Norkus et al. (2006) and visual observation of SEM images. The surface charge on the

developed cathodes may have reduced due to the formation of CuO on the surface and this

requires further investigation.

The developed electrodes were successful in reducing the nitrates from the synthetic sample. A

percentage reduction of nitrate concentrations greater than 98% was achieved by using the

developed cathodes marginally greater than that achieved by the pure Cu cathode. However the

final nitrate concentrations of the treated leachate couldn’t be quantified accurately due to the

limitation of the range in spectrophotometer.

RESULTSElectroless plating

In contrast to the Al substrate, the mild steel electrodes did not show any mass gain of Cu for 0.11 M EDTA

and 0.05 M CuNO3 plating solution at the room temperature. The test was repeated at a steady temperature

of 58oC using the same plating solutions but the mass gain of Cu was insignificant. The concentrations of the

plating solution were increased tenfold up to 1 M EDTA and 0.5 M CuNO3, but still there was no mass gain

in steel electrodes at room temperature nor at 58oC. Since it was unable to get a sufficient plating of Cu on

the mild steel electrodes electrochemical denitrification was carried out using plated Al electrodes only. The

average plating rate of Al increased with the increasing formaldehyde concentration as shown in Fig. 4

Characterization of the electrodes with Scanning electron microscope

Fig. 5: The SEM images of the morphology of the copper plated cathode in bathes (A) 0.1M HOCH, (B)

0.2M HOCH, (C) 0.3M HCOH and (D) pure copper at a magnification of 5000X

The SEM images showed that the size of the grains reduce its size and the size and the number of dimples in

the structure is reduced with the increasing formaldehyde concentration.SEM also images implies that the

electro deposition gives a coarser surface than the pure Cu metal surface. This results shows that the HCOH

concentration has a significant impact on the surface texture.

Characterization of electrodes with cyclic voltammetry

It can be shown that surface area of the electrode could be obtained indirectly by referring to the

cyclicvoltagrams according to Randles-Sevicik equation at 250C.At constant concentration of electrolyte and

the scan rate charge would be directly proportional to the active surface area of the electrode. Fig. 6 shows

the charge vs potential curves obtained for plated electrodes and pure electrodes. According to results

obtained under this experiments shows that Cu has the highest active area.

Denitrification of synthetic leachate

The table 1 shows the nitrate concentrations of the leachate samples before and after the electrochemical

denitrification.The results indicate that the nitrate concentration has dropped during the electrochemical

denitrification and also it confirms that the developed cathodes are more successful than the pure Cu

electrode in denitrification

(A) (B) (C) (D)

Electrode

Initial

nitrate

concentrati

on (ppm)

Final nitrate

concentration

(ppm)

Nitrate

removal

percentage

Pure copper 15 4 73.3%

0.1 M HCOH

electrode 15

Below the

detection limit

(Detection

limit: 0.3

mg/L)

Under range

>98%

0.2M HCOH

electrode15

>98%

0.3M HCOH

electrode 15

>98%

Table 1: Removal of nitrate by pure and developed

electrodes

Characterization • Cyclic voltammetry

• SEM

• EDX

Surface preparation • Shaping

• Cleaning

• Etching

Preparation of

plating bath

Electroless

plating

Denitrification

of synthetic

leachate

Fig. 2: Electroless copper plating

Fig 3. Electrochemical denitrification

Fig. 1: Methodology

REFERENCES Norkus, E, 2006. Obtaining of high surface roughness copper deposits by electroless plating technique. , 51, pp.3495–

3499. Sha, W., Wu, X. & Keong, K.G., 2011. Electroless Copper and Nickel-Phosphorus Plating: Processing, Characterisation and Modelling 1st editio., Limited, Woodhead Publishing

ACKNOWLEDGEMENTS

The authors are grateful to Tokyo Cement Company (Lanka) PLC and

The University of Peradeniya for financing the project