COBALT CONTENT IN SLUDGE EXTRACT PREPARED ACCORDING TO TOXICITY CHARACTERISTIC LEACHING PROCEDURE ("TCLP COBALT")


PART 1: EXTRACT PREPARATION

Procedure for Preparing Biox Plant SOMAT Sludge for Cobalt Analysis, Based on Method 1311 - Toxicity Characteristic Leaching Procedure (For sludge samples of >0.5% dry solids).
Principle:  Extraction of SOMAT sludge with 20 times (by weight) of an acidic solution and filtration. To be followed by spectrophotometric cobalt analysis of the resulting extract described in Part 2.

Materials and Equipment
~2.5 liter extraction bottle with closure.
Rotary agitation device (tumbler).
2 liters of acetic acid solution (5.7 mL of glacial acetic acid per liter, ~0.3% by weight, 0.05 M) pH should be 2.88 +- 0.05. Check before using.  Prepare fresh as needed.  
Filter system with vacuum connection, clean and dry.  
Borosilicate glass filter pads pre-washed with 1N nitric acid, dried.

Procedure:
  Evaluate SOMAT sample to confirm uniform composition (solids without separated water).  If water has separated, remix sample to as homogenous state as possible.
  Weigh out 100 grams of material into the extraction bottle and add 2000 grams of the prepared acid extraction fluid.
 Seal bottle as necessary and place on rotary agitation device at 30 rpm for 18 hours in a room between 21° and 25°C.
 Following the extraction process, filter the material in batches through the acid-washed filter pads.
 Measure the pH of the resultant filtrate.  Acidify as needed with nitric acid to obtain a pH of <2.    This is the TCLP filtrate.  Separate out a portion of the TCLP before preservation and add a 2.0 ppm matrix spike of cobalt to this portion (or whatever the regulatory level for cobalt is). Then adjust pH of the spike portion also.  Refrigerate until time for cobalt analysis.



PART 2: COLORIMETRIC DETERMINATION OF COBALT
Procedure for determining cobalt in TCLP extract from the sludge.
Principle:  complex formation of cobalt (II) ions with 5-dimethylamino-2-nitrosophenol at pH 6-7, accompanied by oxidation to cobalt (III). Extraction of the complex with chlorinated solvent followed by back extraction of unreacted  5-dimethylamino-2-nitrosophenol  with hydrochloric acid.  
Reagents, solutions, solvents

 Concentrated hydrochloric acid (~11.65 M, 1.18 g/mL), Millipore DI water, 5-dimethylamino-2-nitrosophenol hydrochloride, 1,2-dichloroethane, citric acid, trisodium citrate dihydrate, sodium hydroxide 50% w/w solution in water. 

 Cobalt standard, 1 mg/L (1 μg/mL). In a 1 L volumetric flask dilute 1.00 mL of the primary 1 mg/mL standard with water, add ~0.85 mL of concentrated hydrochloric acid, add water to 1 L mark.

 Solution A (NDMP·HCl): 5-dimethylamino-2-nitrosophenol hydrochloride, C8H10N2O2·HCl (CAS# 41317-10-6, FW 202.64 g/mol), 0.005 M in ~0.01 M HCl. Wash 4 oz amber glass bottle with concentrated hydrochloric acid, rinse with Millipore DI water. Weigh 0.10 g of C8H10N2O2·HCl (yellow crystals) in the bottle, add 99.8 g of water and 0.1 mL of concentrated hydrochloric acid. Store refrigerated.

 Citrate buffer. Mix 38.4 g of anhydrous citric acid and ~10 mL DI water, add SLOWLY 47.0 g of 50% NaOH solution, dilute to 100 mL. Measure pH and adjust to 6.2-6.6 using citric acid or 50% NaOH. Alternatively dissolve 58.8 g of trisodium citrate dihydrate (FW 294.10 g/mol) in DI water to make ~100 mL of solution. Add anhydrous citric acid (about 2.8 g) to reach pH of 6.2-6.6.

 Hydrochloric acid 1:2 (~ 3.9 M): place 65 g of water in 4 oz bottle and add 38.4 g of concentrated hydrochloric acid.

 1,2-Dichloroethane: use as received, store in an amber glass bottle.


Calibration Procedure
  Place 0.5 mL of 1.0 μg/mL cobalt standard in a 100 mL Erlenmeyer flask, add DI water to 30 mL. Record standard volume.
 Add 1.5 mL of citrate buffer.
 Add 1.5 mL of NDMP·HCl solution
 Mix thoroughly and wait 10 minutes
 Add 5 mL of 1,2-dichloroethane and mix thoroughly for  one minute
 Allow chlorinated solvent to settle, collect with pipette into 20 mL vial, add 5 mL of 1:2 hydrochloric acid, mix thoroughly.
 Collect washed chlorinated solvent with with pipette and run through a syringe with syringe filter and filtering paper to remove excess water. Collect filtrate.
 Measure absorbance versus pure 1,2-dichloroethane at 456 nm and at 500 nm in 10 mm path cuvette. Record the result. 
 Repeat for 1.0, 2.0, 2.5, 3.0 mL of cobalt standard
 Run blanks for DI water, blank extract.
 Calculate calibration lines A456 = a456m + b456, and A500 = a500m + b500 using least squares method, where m is mass of cobalt introduced with the standard in μg. Intercept at b456   is expected to be slightly positive due to residual unrecated NDMP.

Procedure
 Place 1-30 mL of extract containing about 3 μg of cobalt in a 100 mL Erlenmeyer flask, add DI water to 30 mL, if needed. Record sample volume.
 Add 1.5 mL of citrate buffer.
 Add 1.5 mL of NDMP·HCl solution
 Mix thoroughly and wait 10 minutes
 Add 5 mL of 1,2-dichloroethane and mix thoroughly for  one minute
 Allow chlorinated solvent to settle, collect with pipette into 20 mL vial, add 5 mL of 1:2 hydrochloric acid, mix thoroughly.
 Collect washed chlorinated solvent with with pipette and run through a syringe with syringe filter and filtering paper to remove excess water. Collect filtrate.
 Measure absorbance at 456 and 500 nm versus pure 1,2-dichloroethane in a 10 mm path cuvette.
 If absorbance exceeds calibration range, repeat the procedure using smaller sample amount. If absorbance is comparable to blank reading (intercept of the calibration plot), increase sample volume and repeat previous steps.
 Calculate cobalt content in μg using calibration data.
 Calculate cobalt TCLP concentration using result from (9) and volume of the sample from (1).



