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Stabilization/Solidification - 8.2 Case Study #2

 8.2 Case Study #2: Solidification of liquid waste contaminated with antimony, New Orleans, Louisiana (Conner, 1990; Conner, 2004), 1976

 8.2.1 Background

Although this case was conducted more than 30 years ago, it is still a representative application of cement-based S/S technology (Conner, 1990). Its chemistry, delivery system, and operation are still very proper by today's standards. The waste was generated from a chemical plant in West Virginia and transported to New Orleans. It was temporarily tanked and prepared to be ocean-dumped, but ocean-dumping was stopped when 4,000,000 gallons of waste remained to be disposed of. The waste contained high levels of dissolved organics, salts and dissolved antimony. It was solidified and waited for a series of tests to verify that it was suitable for local, sanitary landfill as a non-toxic solid. (Conner, 2004)

8.2.2 Treatability Studies

"The waste was a low-viscosity, semi-clear solution with very little suspended solids", according to Conner (2005). Table 8.2 gives the results of untreated waste analyses. The state of Louisiana would allow the disposal of this waste in a local landfill if it could be treated to become a stable, portable solid with limited antimony leachability. (Conner, 2004) 

 

Table 8.2: Analysis of untreated waste - case study #2 

Contaminant

Concentration  (wt%)

Ethylene glycol

6.6

Diethylene

0.2

Sodium terephthalate

2.5

Sodium chloride

8.3

Sodium sulfate

0.9

Ammonium chloride

1.1

Antimony

0.0234

                         Source: Conner, 2004

The S/S process was performed using a combination of Portland cement and sodium silicate solution to quickly set and harden the liquid waste. A pretreatment process with hydrated lime was used to precipitate or remove some of the dissolved organics. Pretreatment helps in avoiding organic interference with cement setting and reducing the usage of S/S reagents. (Conner, 2004)

The operational parameters for this project are listed below in Table 8.2.2 (Conner, 2004).

Table 8.2.2 Operational Parameters for New Orleans Remediation Case Study

Volume Treated

4,000,000 gallons

Treatment Rate

130,000 Gallons/Day average

Time

Spring 1976

Treatment Cost

$0.167/gallon

Disposal Method

Sanitary landfill, daily cover material

          Source: Conner, 2004

8.2.3 Delivery System 

The delivery system for this case is shown in Figure 8.2. It consists of two units: a pretreatment unit and an S/S unit. The primary difference of this system is that the treatment units are completely mobile and are largely self-contained. (Conner, 2004)

 8-1

Figure 8.2: Schematic drawing of the treatment units in Case study #2 (Conner, 2004)

 

8.2.4 Operations and Results 

The immediately treated waste was quite fluid and needed to be temporarily stored in an impoundment until it was solidified. After all the waste was treated, the final sampling was done, test results were obtained and approved by the state, and the solid was excavated and transported to the final disposal site. (Conner, 2004) 

For treated waste, strength tests with a penetrometer and a vendor-developed column-leaching test were carried out. The test results are listed in Table 8.2.4.

 

Table 8.2.4 Comparison of Treated Waste to Raw Waste Analyses – Case Study #2  

Contaminant

Concentration in Raw Waste (mg/kg)

Concentration in Treated Waste (mg/L)

Ethylene glycol

66,000

NM

Diethylene glycol

2,000

NM

Sodium terephthalate

25,000

NM

Sodium chloride

8,300

NM

Sodium sulfate

9,000

NM

Ammonium chloride

11,000

NM

Antimony

234

0.1

Chloride

NRa

160.0

Sulfate

NR

5.0

Chemical oxygen demand

NMb

350.0

a NR: Not measured and reported separately as the anion, but present in compounds listed above.

b NM: Not measured.

             Source: Conner, 2004 

Although the results cannot be directly compared with current Toxicity Characteristic levels (< 1.15mg/L), according to Conner’s (2004) experience, they are likely to meet the limits. Also, the chloride, sulfate leachate concentrations and chemical oxygen demand (COD) are very small. (Conner, 2004). The compressive strength of the solid S/S product is as high as 4 to 5 tons/ft2 (~75 psi). (Conner, 2004). These properties of the S/S products allow them to be disposed in a local sanitary landfill. The properties allowed the products to be used as daily cover material, which is a higher end use. (Conner, 2004)

 

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