Delivery Of The Technology

For site remediation applications, the technology is delivered by means of a mobile system that can be operated under a TTU (Transportable Treatment Unit) permit. The equipment is versatile and self-contained, requires a relatively small space, and can be made operational on a site within two to three working days.

The principal elements of the treatment system, shown schematically in Figure 1, consist of the feeder, magnet, screen, pug mill mixing plant, and polysilicate blending unit. The actual equipment used in the latter two elements is shown in Figure 2. These unit operations are operated as an in-line continuous system with a throughput of 100-125 tons/hr.

A brief description of the system (Figure 1 ) follows. Soil requiring treatment is taken from stockpiled material with a front-end loader and fed into a variable-speed feeder equipped with a set of grizzly bars to remove large tramp material. In some cases, to improve material handling and eliminate certain objects that could fall through the grizzlies (which could cause tears in the feeder belt or jams in the feeder, resulting in excessive equipment maintenance downtime), stockpiled material is prescreened with a short residence time mobile screen. After the material exits the feeder, it passes under a cross belt magnet to remove any ferrous material that may be present. (This fraction is common in scrap yard remediations.) The material then enters a triple-deck screen, where the large oversize fraction consisting of pieces of concrete, asphalt, wood, etc., is removed on the top deck. After the middle fraction (i.e., smaller rocks, stones, nonferrous metals, etc.) is removed, the remaining material is the undersize soil that is suitably conditioned for treatment. The feed rate of the material entering the feed hopper on the treatment unit is recorded by a certified belt scale.

The polysilicate additives and mixing process are configured into two mobile treatment units. The mixing unit (Figure 2) consists of two feed hoppers, a twin-screw pug mill, a ce-mentitious material storage silo, and a discharge conveyor. The silo, capable of storing approximately 50 tons of material, is hydraulically elevated after the unit arrives on the site. Although a diesel engine generator system is mounted on the mixing trailer to provide a self-contained source of power, the demands of the ancillary equipment may require the use of a separate mobile generator on the site. The polysilicate delivery system is contained in a separate trailer. A 2000-gal buffer tank allows the polysilicate-containing water blend to be delivered to a spray nozzle system at the point where the soil enters the pug mill. The polysilicates are added to the buffer tank by means of calibrated metering pumps connected to four 250-gal tanks. Polysilicate in 55-gal drums can be directly pumped into these tanks from outside the trailer. Typically, water enters the buffer tank directly from an on-site hydrant. Appropriate instrumentation allows for the measurement of the flow rates of all water and chemicals entering and exiting the chemical delivery system. Thus, along with the measurement of the soil throughput, a complete mass balance can be performed on the system.

During operation, material requiring treatment enters the rear of the twin-screw pug mill. The diluted polysilicate blend is sprayed onto the feed soil. Intensive wetting of the soil with the polysilicates occurs in the first half-portion of the mixer. The cementitious material is

Table 1 Elements of the Metals Treatment Database

Generator Waste Physical

Laboratory I.D. information classification characteristics

Generator Address Site Location

Waste type Waste code Character Treatment date

% Moisture Density

Comprehensive strength

Treated size

Waste treated (g)

Treatment Extraction reagents information Pre- and post-treatment concns.

Silicate 1 (g)

Ext. date (totals)

Ag STLC

Ni STLC

Silicate 2 (g)

Ext. date (TCLP)

Ag TCLP

Ni TCLP

Cement (g)

Ext. date (STLC)

AgTTLC

Ni TTLC

Cement type

Al STLC

Pb STLC

Lime (g)

Al TCLP

Pb TCLP

Lime type

A1TTLC

Pb TTLC

Fly ash (g)

As STLC

Sb STLC

Fly ash type

As TCLP

Sb TCLP

Kiln dust (g)

AsTTLC

Sb TTLC

Kiln dust type

Ba STLC

Se STLC

Polysulfide (g)

Ba TCLP

Se TCLP

Polysulfide type

BaTTLC

Se TTLC

Phosphate (g)

Be STLC

T1 STLC

Phosphate type

Be TCLP

T1 TCLP

Acid (g)

Be TTLC

T1 TTLC

Acid type

Cd STLC

V STLC

Base (g)

Cd TCLP

V TCLP

Base type

Cd TTLC

V TTLC

Oxidant (g)

Co STLC

Zn STLC

Oxidant type

Co TCLP

Zn TCLP

Reductant (g)

Co TTLC

Zn TTLC

Reductant type

Cr(III) STLC

CaSTLC

Other 1 (g)

Cr(III) TCLP

Ca TCLP

Other 1 type

Cr(III) TTLC

Ca TTLC

Other 2 (g)

CrfVI) STLC

Cl STLC

Other 2 type

Cr(VI) TCLP

Cl TCLP

Cr(VI) TTLC

CI TTLC

Cu STLC

Fe STLC

Cu TCLP

Fe TCLP

Cu TTLC

Fe TTLC

F TTLC

Mg STLC

F STLC

Mg TCLP

F TCLP

Mg TTLC

Hg TTLC

Na STLC

Hg STLC

Na TCLP

Hg TCLP

Na TTLC

Mo STLC

Final dry wt.

Mo TCLP

pH solid

Mo TTLC

pH extract

Table 2 Total Metal and Pre- and Posttreatment Concentrations for Metal Groups 1-5

Extraction procedure

Character

Units

Arsenic Copper

Lead

Nickel

Cadmium

Zinc

Metal system 1

Totals 3050

Initial

mg/kg

2 16,300

2

1.24

0.01

70

STLC

Initial

mg/L

0.005 589

0.27

1.52

0.01

0.01

STLC

Treated

mg/L

0.001 11.23

0.02

0.88

0.01

0.01

Metal system 2

Totals 3050

Initial

mg/kg

3217 1359

21

29

2

398

TCLP # 1

Initial

mg/L

140 1.11

0.06

0.1

0.01

2.2

TCLP #2

Treated

mg/L

0.09 0.12

0.05

0.1

0.01

0.00 3

Metal system 3

Totals 3050

Initial

mg/kg

0.001 3917

770

30

40

5400

STLC

Initial

mg/L

0.0001 383

72

2.89

0.28

915

STLC

Treated

mg/L

0.0001 0.88

0.075

0.01

0.005

21.05

Metal system 4

Totals 3050

Initial

mg/kg

N/A 350

537

92

4.95

1,012

STLC

Initial

mg/L

N/A 19.01

31.99

2.56

0.46

87.04

STLC

Treated

mg/L

N/A 7.28

0.62

1.64

0.005

0.84

Metal system 5

Totals 3050

Initial

mg/kg

2,759 1,627

1,550

470

48

325

TCLP #2

Initial

mg/L

158.3 34.7

0.33

41.25

1.54

15.7

TCLP #2

Treated

mg/L

0.068 0.075

0.28

20.91

0.005

Sod

Requiring

Variable

Treatment

Grizzly

Speed

Bars

Feeder

Large

Rejects

Cementitious Material Storage

Mitigated Sod

Figure 1 Schematic diagram of soil treatment system.

Treated Soil Curing

Middle Fraction

Polysilicate Blending Unit

Silicates

Treatment Unit

Figure 2 Equipment used in the delivery of the STS technology.

introduced at the midpoint of the mixer. The feed rate can be adjusted by controlling the variable-speed drive on the silo rotary vane feeder. The residence time in the mixer is controlled by the blade angles. For soil, a 22° blade angle is used in the first half of the mixer to enhance retention (i.e., increase the contact time between the silicates and the material). In the section after the cementitious material is added, the blade angles are set at approximately 45° to enhance mixing and removal of the treated material from the chamber. As the treated material exits the pug mill unit, a radial stacking conveyor piles the material. The process is complete after the material has cured in the stockpiles. The treated stockpiles typically are turned with a front-end loader on a daily basis for several days. A Bomag unit can also be used to cure treated material. Here, the material is arranged in 3-4-ft lifts. After the material has partially set, the Bomag unit traverses the lift, creating suitably sized material.

The final aspect of the treatment includes the sampling and subsequent analytical evaluation of the cured material. This involves obtaining representative samples from treated stockpiles and subjecting the material to an extraction test. If the EPA TCLP test is used, the treated material (crystalline cementitious matrix) is extracted with a sodium acetate-acetic acid buffer solution. In this process, metallic elements can be leached from the matrix to form metal acetates. As shown below, the final extraction product is an equilibrium mixture of metal poly-silicates, metal acetates, acetic acid, metal hydroxides, metal oxides, etc.

a CHjCOCr + b H+ +cNa+ + dH20 + e MfOH), + /Ca(OH)2 + g metal polysilicates + •■•—»

h (CH3COO),M + i CHjCOONa + j CH3COOH + k H20 + / M(OH)x + m Ca(OH)2 + n NaOH + o Ca3(C6H507)2 + p metal polysilicates

Thus, in order for a treatment to be successful with regard to the TCLP test, a stable matrix must be created that resists the attack of the aggressive leaching fluid, i.e., one in which only negligible quantities of soluble metallic elements are present. Upon completion of the analytical data, the treated friable material can then be backfilled on the site with conventional earth-moving equipment.

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