TREATMENT OF COMPLEX ELECTROPLATING WASTE BY “ZERO DISCHARGE by StuartSpruce

VIEWS: 25 PAGES: 3

									   TREATMENT OF COMPLEX ELECTROPLATING WASTE BY “ZERO
                  DISCHARGE” TECHNIQUE.
                               B. Q. Khattak, P. Ram Sankar and A. K. Jain
                         Chemical Treatment lab, ACE&F Division, RRCAT, Indore


   bqk@rrcat.gov.in



Abstract                                                        at a concentration of 0.8 mg/litre kills gold fish within 24
Surface treatment processes generate lot of liquid waste,       hours. Similarly metabolic activities of mammals are
which contains toxic substances and are potentially             affected by heavy metals. Chemical transformation by
harmful to the living beings. It is extremely difficult to      sodium hydroxide could not be continued successfully as
treat the pollutants where processes and frequencies are        it is ineffective in removing anions and difficulties in
not fixed. In Chemical Treatment Facility of RRCAT              controlling the pH of the effluent during treatment.
surface treatment processes are user dependent and makes        Large variation of pH during treatment resulted in the re-
the electroplating waste very complicated. Initially the        dissolution of heavy metals that are precipitated. Ion
waste was treated by simple chemical transformation             exchange method could remove anions and cations from
technique in which heavy metal ions are converted to            the waste but anions such as fluoride and nitrate
hydroxide precipitates. Non metallic ions that contribute       frequently exhausted the polymeric structure, resulting in
much to the plating waste could not be treated by this          the very short service life. Phosphate ions present in
process. To remove maximum possible pollutants, many            waste developed chocking of exchange column due to the
experiments were conducted on the laboratory scale.             formation of calcium phosphate. A pre-treatment plant in
Based on those results, a pilot ion exchange plant of           combination with clarifier – platter and high pressure
various resins was introduced in the process to achieve         filters works effectively for the treatment of plating waste.
disposal quality effluent. Anionic load of Phosphate,           This treated waste can be reused after passing through a
Nitrate and fluoride caused frequent anionic bed                reverse osmosis membrane and ion exchange columns. In
exhaustions and polymeric network damaging. To avoid            this paper we discuss about the present set up established
this phenomenon a new setup was designed. This pre              and future plans for zero discharge.
treatment has the capacity to treat 500 litres per hour
connected to a platter with clarifier followed by high                           EXPERIMENTAL
pressure carbon and pebbles filters. Analysis of these ions     Artificial effluent was prepared to conduct experiments in
was carried out on the advanced ion chromatography              laboratory with maximum expected anionic and cationic
system and is found free of toxic metals, phosphate and         concentrations. The concentrations of chloride, sulphate
fluoride. This effluent can be reused by adding a reverse       and phosphate were found as 9954, 5308 and 8965 ppm
osmosis system followed by ion exchange system to               respectively after analysis. Concentrations for cationic
produce good quality de mineralized water needed for            pollutants for tin, zinc, copper, nickel, iron and aluminium
surface treatment activities.      In this paper we describe    were 200, 406, 382, 414, 500 and 100 ppm respectively.
the existing status of effluent treatment facility and future   Glass tubes having diameter of 4cm and length 100 cm
plans for achieving “zero discharge”.                           were used for preparing ion exchange columns. Strong
                                                                cationic resin in sodium form and strong anionic resin in
                 INTRODUCTION                                   chloride form were used as exchange medium.
   Surface treatment and modification of components used        Experiments were conducted for calculating the treated
in accelerators is essential to achieve ultra high vacuum       volume of prepared effluent per millilitre of resin. It was
and other functional requirements such as conductivity,         found that 1ml of strong cationic resin is capable of
lubricity and corrosion resistance etc. Chemical cleaning       removing the cations from 85.7 ml of effluent whereas 1
and electro deposition techniques are preferred over            ml of strong anionic resin removes anions from 18.7 ml of
physical deposition methods due to its simplicity and           effluent, with a regeneration cycle ratio of 4. To reduce
versatility in handling big components. The major               the regeneration cycle ratio, pre-treatment with alkali and
disadvantage of these processes is the generation of large      alkaline earth hydroxides was introduced followed by ion
volume of liquid waste which needs proper treatment             exchange treatment. To find out ionic concentrations
before disposal. The major cations and anions present in        standard volumetric, ion selective, spectrophotometric
the effluent are nickel, copper, iron, aluminium, zinc,         and ion chromatographic techniques were used.
chromium, nitrate, phosphate, sulphate, chloride and
fluorides. Plating waste has a marked impact on aquatic
life and human beings. Copper when present in the waste
         RESULTS AND DISCUSSION                                installed with calcium hydroxide as the precipitant.
                                                               Analysis of the treated effluent for various parameters is
Reactions involved in various treatment methods
                                                               shown in table 5. This treated effluent is then passed
mentioned above for removing the metallic and non
                                                               through the ion exchange unit shown in figure 3.
metallic ions are as follows;
                                                               Table 4: Conversion of effluent to deionized water
i.       With sodium hydroxide precipitation;
          M n+ + n OH−→ M (OH)n
                                                               Parameters           After ion exchange   After mixed bed
ii.      With Calcium hydroxide;
          Along with the reaction (i) the following anionic    pH                   10.2                 6.8 – 7.4
reaction also takes place;                                     Conductivity         30-50 S/cm           0.2 – 0. 7 S/cm
         2PO 4 −3 + 3Ca +2 → Ca 3 (PO4 )2 (precipitate)        Total cations        1 – 10 mg/L          BDL
         2F − + Ca +2       → CaF2 (precipitate)               Chloride             1-4 mg/L             BDL
iii.     Ion exchange reactions;                               Sulphate             2-6 mg/L             BDL
a.       cationic reaction;                                    Phosphate            1-2 mg/L             BDL
          R− — H + + M n+ → R n M + n H +
b.       Anionic reactions;
          R + — OH− + Nm n− → R n —Nm + n OH –

Table 1: Variation in effluent quality after passing through
ion exchange resin columns

Parameters          Before treatment     After ion exchange
pH                  <1.0                 10.2
Conductivity        >50000 S/cm          50 – 80 S/cm

The volume of effluent treated per millilitre of strong
cationic and strong anionic resin with and without alkali
treatment was also calculated to find out the regeneration
ratio cycle. The increase in treated volume of effluent per
millilitre of resin after alkali treatment is due to removal
of metallic and non-metallic ions by precipitation as
hydroxides, phosphates and fluorides. Analysis of the          Figure 1 clarifier-platter systems for lime treatment
treated effluent was carried out to determine the quality of
water and is shown in table 3. It was found that the
treated water quality was better than raw water.

Table 2: Treated volume effluent per ml of resin

Resin type          Without    alkali    After      alkali
                    treatment.           treatment.
Strong cation       85.7 ml              173 ml
Strong anion        18.7                 147 ml

Table 3: Comparison of raw and treated water quality

Parameters          Raw water            After ion exchange
pH                  8.2 – 8.4            10.2
Conductivity        390 - 450 S/cm       30-50 S/cm
Total cations       180 – 220 mg/L       1 – 10 mg/L           Figure 2 Filtration System for treated effluent
Chloride            20-24 mg/L           1-4 mg/L
Sulphate            12 – 20 ng/L         2-6 mg/L
                                                               Conclusion: Heavy metals, Fluorides and Phosphates
                                                               present in the plating effluent can be removed efficiently
If a mixed bed column (3:1 anionic to cationic) is added
                                                               by using calcium hydroxide as precipitant and in
after ion exchange column, the quality of the treated
                                                               combination with ion exchange plant. Plating waste thus
effluent was improved further as shown in table 4. Based
                                                               obtained from lime treatment system is suitable for
on the laboratory scale experiments, a continuous
                                                               disposal as per the guidelines of APHA, ASTM and ISI
treatment plant with clarifier-platter and filtration system
                                                               standards. Moreover, installation of a softener and
having a capacity to treat 500 litres per hour (fig. 1) was
reverse osmosis set up to the existing system, we can
convert complex electroplating waste into good quality
water that can be reused again for electroplating activities
leading to zero discharge technique.

Table 5: Analysis report after clarifier – platter using
Calcium Hydroxide:

Parameters                     Results
Appearance                     Transparent
Turbidity                      2.0 NTU
Electrical conduct.            1160 S/cm
pH                             8.6
FMA                            Nil
Total alkalinity               246 mg/L
p- alkalinity                  35 mg/L
Bicarbonate                    205 mg/L
Carbonates                     30mg/L                                    Fig.3: Ion exchange treatment plant
Sulphate                       374 mg/L
Chloride                       63 mg/L
                                                               Acknowledgement: The authors wish to acknowledge
Total hardness                 480 mg/L
                                                               Shri.S. N. Vyas, Ex-head, chemical treatment laboratory,
Iron                           0.27 mg/L
                                                               for his constant support and encouragement. Authors are
Copper                         BDL                             thankful to Shri. S. K..Sharma of chemical treatment
Nickel                         BDL                             laboratory, for his sincere efforts in operating the
Dissolved Oxygen               6.5 mg/L                        treatment system and for generating the necessary data.
SS                             28 mg/L
TDS                            1048 mg/L
COD                            10 mg/L                         References:
BOD                            Nil                             1. Electro deposition, A move towards zero waste
Residual chorine               Nil                             disposal technique, Internal report reference no
Phosphate                      Nil                             CAT/2001/11.
Fluoride                       Nil

								
To top