IWC 12

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# Shale Gas Produced Water Pretreatment for

Barium and Radium Removal

JAMES SILVA, HOPE MATIS,

WILLIAM KOSTEDT IV, and VICKI WATKINS

GE Global Research Center, Niskayuna, NY

IWC

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KEYWORDS: Marcellus, hydrofracturing, NORM, radium, ion exchange, adsorption,

Radium

‐ specific complexer, shale gas, pretreatment

ABSTRACT

A GE survey of 6 shale gas wells in Pennsylvania and a DEC survey of 13 shale gas wells

in New York show that much of the Marcellus flowback and produced (“frac”) water

contains significant concentrations of barium and naturally occurring radioactive

materials (NORM), particularly radium. Although up to about 95% of Marcellus frac

water has been reused for subsequent hydrofracturing activities, this practice is not

sustainable. For example, when the price of natural gas decreases, the rate of

hydrofracturing slows and the demand for source water decreases. However, the

supply of produced water from existing wells continues, and can exceed the demand for

source water blendstock. Rather than trucking excess produced water into Ohio for

deep

‐ well injection, 80

‐ 95% may be recovered as distilled water by a combination of

evaporation (mobile or fixed) and crystallization of a NaCl product (which is more

suitable for centralized facilities). The NaCl product must pass TCLP with respect to

barium in order to be salable or disposable in a RCRA

‐ D landfill. We evaluated seven

pretreatment processes to remove barium and radium from Marcellus produced water:

ion exchange, nanofiltration, sulfate precipitation, carbonate precipitation, a modified

carbonate precipitation process, adsorption onto a radium specific sorbent, and

adsorption onto MnO 2

. This work describes the materials and disposal costs for each

process and shows laboratory validation results for two pretreatment processes.IWC 12

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INTRODUCTION

Since 2007, shale gas has emerged as a

“game changer” for the United States’ natural

gas market, accounting for 23% of domestic

production in 2011. The Pennsylvania

Marcellus is one of the most active shale gas

plays in the United States, with over 1750 new

shale gas wells drilled in 2011. The volume of

flowback and produced water in Pennsylvania

in 2011 from shale gas production was 24.1

MM bbl 1

. A potential limitation to further

development of the Marcellus is the high

disposal cost of hydrofracturing flowback and

produced water. The high TDS level in

produced water makes it less desirable than

earlier flowback water for reuse in subsequent

hydrofracturing activities. Therefore, this paper

is focused on pretreatment and recovery of

high

‐ TDS produced water. In addition to high

salinity and hardness levels (Mg, Ca, Sr, Ba),

much Marcellus produced water also contains

significant levels of naturally occurring

radioactive materials (NORM), particularly

radium

‐ 226 ( 226 Ra). Produced water from oil

and gas production has traditionally been

disposed of by deep

‐ well injection 2

. However,

there are only 7

‐ 8 deep

‐ well injection facilities

(UIC 3 ) in Pennsylvania, with an average

injection rate of less than 1,000 barrels per

day 4

. For Pennsylvania Marcellus produced

water, there are therefore three disposal

options: (1) it may be reused as blendstock in

subsequent drilling and hydrofracturing jobs,

(2) it may be trucked to Ohio for UIC disposal at

a cost of $10

‐ 12/bbl for transportation and

disposal 4

, or (3) it may be thermally recovered

as distilled water and (optionally) a solid salt

product.

Table 1 shows the rate of Pennsylvania

Marcellus frac water production and disposal

by UIC. The percentage disposal by UIC was 6

‐

8% during 2011, which implies that 92

‐ 94% was

reused in subsequent hydrofracturing jobs.

However, this high reuse rate is not

sustainable. For example, when the rate of hydrofracturing decreases (e.g. due to falling

natural gas prices), the demand for

hydrofracturing source water decreases.

However, the supply of produced water is

proportional to the number of wells in

production, which has been growing steadily.

When the supply of produced water exceeds

the demand for source water blendstock,

produced water must be either disposed of by

UIC or thermally recovered.

The purpose of this study is to identify

pretreatment technologies that enable

economic recovery of distilled water and a

salable or disposable solid salt product from

high

‐ TDS Marcellus shale gas produced water

containing elevated levels of barium and

radium. The high TDS levels in the produced

water limit recovery options to thermal

processes (evaporation and crystallization).

Pretreatment technologies include both

softening (primarily barium removal) and

NORM removal.

Table 1. Marcellus 2011 Frac Water Production

and Disposal (MM bbl)

Jan

‐ Jun July

‐ Dec 2011

Flowback 3.75 11.22 14.97

Produced 4.69 4.46 9.15

Total 8.44 15.68 24.12

To UIC 0.52 (6.1%) 1.27 (8.1%) 1.79 (7.4%)

NORM DISPOSAL OPTIONS

All pretreatment processes seek to

concentrate Ra and Ba that are present in the

raw produced water into a small stream that

can be disposed of economically. As discussed

by Veil 2

, disposal options for waste streams

that contain 226 Ra are limited. For disposal as

nonhazardous solid waste in a RCRA

‐ D 5 landfill,

the material must have a 226 Ra activity below 5

‐

50 pCi/gm (varies by state). The 226 Ra limit for

Pennsylvania is 25 pCi/gm. In addition, the

solid waste must pass TCLP with respect to

barium 6

. Pennsylvania has no facilities for solid

waste that contains greater than 25 pCi/gmIWC 12

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226 Ra. Such material must be either blended

with sufficient non

‐ radioactive solid waste to

meet the RCRA

‐ D specification or shipped out

of state as low

‐ level radioactive waste (LLRW)

or as NORM waste. Examples of NORM waste

disposal operators include LOTUS (LLC) and

Newpark Resources (both of Texas). Newpark

Resources disposes of NORM sludges by

injection into Class II disposal wells after

particle size reduction and slurry preparation.

EnergySolutions, Inc. (Utah) disposes of LLRW,

which can contain up to 10 nCi/gm 226 Ra.

Alternatively, pretreatment processes that yield

aqueous concentrate byproducts containing Ba

and Ra may be disposed of by UIC. Table 2

shows typical costs for each disposal option

(excluding transportation to disposal site).

Table 2. Disposal Costs

Facility $/bbl $/short ton

Class II UIC 2.20 11.50 a

RCRA

‐ D Landfill 13.50 b 50

NORM Waste 125

‐ 300 400

‐ 960 c

LLRW 1120 3600 c

a aqueous concentrate specific gravity=1.094

b 45 wt% BaSO 4 sludge (bulk sp. gr.=1.75)

c Dry BaSO 4 sludge (bulk sp. gr.=1.79)

THERMAL WATER AND SALT RECOVERY

Table 3 shows the “design case”

produced water composition, which is based on

median composition measurements from seven

produced water samples that we obtained (six

from the Pennsylvania Marcellus and one from

the Texas Barnett). As shown in Figure 1,

current produced water recovery technology

comprises lime pretreatment to precipitate

magnesium as Mg(OH) 2 , iron as Fe(OH) 3 , and

manganese as MnO 2

. Figure 1. Current Thermal Water Recovery

Process (design case feed composition)

This pretreatment also removes

suspended solids from the raw produced water,

which often contain NORM. The pretreatment

sludge may be disposed of as nonhazardous

solid waste or as NORM waste, depending on

the 226 Ra activity in the sludge. The pretreated

produced water is thermally evaporated to

obtain distilled water and a brine concentrate.

For the design case, 56% of the produced water

is recovered as distilled water. This process

also yields an aqueous concentrate, which may

be further evaporated in a crystallizer to yield a

salt product or disposed of by UIC. Both

pretreatment and evaporation processes are

currently available as mobile or fixed

operations.

Table 3. Produced Water Compositions

(all quantities mg/L except where noted)

Design

Case Well

‐ 4 a Well

‐ 5 b

TDS 132,460 68,439 149,188

Na + 35,000 19,200 39,000

Mg ++ 800 570 1,000

Ca ++ 9,500 5,360 13,000

Sr ++ 2,500 1,290 2,600

Ba ++ 6,200 32 3,500

Fe ++ 50 55 32

Mn ++ 3 1.7 2.7

Cl ‐ 78,407 41,845 90,014

SO 4 = 0 57 <5

SiO 2 0 29 39IWC 12

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TSS 200 62 520

226 Ra * (pCi/L) 5,000 4,600 5,600

a For MnO 2 adsorbent tests

b For modified carbonate precipitation tests

To achieve high water recovery (e.g. 80

‐ 95%), it is necessary to generate a solid salt

(NaCl) product. For use as road salt, the solid

salt product must pass TCLP 7

, which includes

the requirement that the TCLP extract of the

salt product contain less than 100 mg barium/L.

Although there is currently no radium

specification for road salt in either New York or

Pennsylvania 8

, it is assumed that the radium

activity in road salt made from purified

produced water must not exceed that of road

salt currently in use, which is on the order of 1

‐

2 pCi/gm.

Figure 2 shows multiple options for high

water recovery from produced water. After

lime treatment, a fleet of mobile evaporators

or a central evaporator concentrates produced

water, yielding distilled water and concentrated

produced water. The lime

‐ treated produced

water may be pretreated to remove barium

and radium prior to evaporation (option 1), or

the concentrated produced water may be

pretreated to remove barium and radium

(option 2).

Figure 2. Schematic Diagram of Produced

Water Recovery Process

Ba, Ra REMOVAL PRETREATMENT OPTIONS We analyzed seven pretreatment

processes for barium and radium removal from

produced water: ion exchange, nanofiltration,

sulfate precipitation, carbonate precipitation, a

modified carbonate precipitation process,

adsorption by a radium specific complexer, and

adsorption by MnO 2

. For each process, a

material balance was calculated to enable

estimation of materials and disposal costs.

Table 5 shows a summary of the

pretreatment options and the cost of materials

and concentrate disposal for each option. Each

process option is discussed below.

ION EXCHANGE: Chelating ion exchange is

widely practiced in the chlor

‐ alkali industry to

remove divalent metals such as calcium and

magnesium from concentrated NaCl solutions.

However, the design case produced water has

such a high concentration of Group II metals

(equivalent to 13,800 mg Ca ++ /L) that a

chelating ion exchange resin bed would be

exhausted after processing approximately one

‐

half bed volume of evaporator concentrate.

The cost of regeneration chemicals and disposal

of waste streams by UIC is prohibitive

($6.30/bbl raw produced water). Further, the

volume of ion exchange resin rinse water,

which is needed after both acid treatment and

caustic treatment, exceeds the volume of raw

produced water. This technique is therefore

not recommended for pretreating Marcellus

produced water.

NANOFILTRATION: Using WinflowsTM

membrane system design software 9

, we

simulated a nanofiltration process to remove

divalent cations from lime

‐ treated produced

water (not evaporator concentrate). Using a

feed pressure upper limit of 600 psig, we found

that a maximum of 30% water recovery was

possible for the design case. The estimated

cost for transportation from central

Pennsylvania to Ohio and UIC disposal is about

$11/bbl. The cost of transport and UIC disposal

of the nanofiltration concentrate is thus about

$7.70/bbl raw produced water, which isIWC 12

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prohibitive. This approach is not recommended

for Marcellus produced water pretreatment.

SULFATE COPRECIPITATION: As discussed

earlier 10

, sulfate treatment is a highly effective

method for removing barium and radium from

brine solutions. Further, the cost of sodium

sulfate is modest (assumed $134/short ton),

which is about $0.15/bbl produced water for

the design case. Contacting lime

‐ treated

produced water or evaporator concentrate

with sodium sulfate coprecipitates a solid

solution of (Ba,Ra)SO 4 , radiobarite. Lab

precipitation experiments showed that as

sulfate is added to produced water samples,

radium and barium precipitate as (Ba,Ra)SO 4 in

amounts proportional to the barium and

radium concentrations in the produced water.

Thus, sulfate precipitation is not selective

toward either cation, which confirms early

work by Doener and Hoskins 11

.

We estimated the 226 Ra activity in

sludge resulting from sulfate treatment by a

simple material balance in which a

stoichiometric amount of Na 2 SO 4 is added to

produced water (or evaporator concentrate) to

yield (Ba,Ra)SO 4

. Each point on Figure 3

represents a barium concentration and radium

activity in the raw produced water. Each line

represents a constant 226 Ra activity in the

sludge (45 wt% solids) resulting from

stoichiometric addition of Na 2 SO 4 to raw

produced water compositions represented by

points on the line. For example, the 226 Ra

activity in sludge resulting from the design case

produced water (6,200 mg/L barium and 5,000

pCi/L 226 Ra) is 213 pCi/gm, which is just above

the 200 pCi/gm line. Raw produced water

sample compositions from a GE survey 13 of

Pennsylvania Marcellus wells are plotted for

comparison. The estimated cost for materials

plus transport (PA to TX) and disposal of dried

sludge in a NORM waste facility is about $1.20

‐ 2.00/bbl raw produced water. For comparison,

the cost for sulfate treatment and RCRA

‐ D

landfill disposal of sulfate sludge that is below

25 pCi 226 Ra/gm is about $0.33/bbl raw produced water 13

. Despite the relatively high

disposal cost, sulfate coprecipitation has two

key advantages. First, the (Ba,Ra)SO 4 product is

chemically stable; it is insoluble in both HCl and

NaOH. Secondly, sulfate coprecipitation is a

well

‐ established process.

0 1000 2000 3000 4000 5000 6000 7000 8000

0 5000 10000 15000 20000 25

50

100

200

500

SamplesRaw produced water226Ra activity, pCi/L

Raw produced water [Ba], mg/L Wet Sludge 226 Ra activity, pCi/gm

(45 wt% solids) Design

Case

Figure 3. Produced Water Ba, Ra Map

CARBONATE PRECIPITATION: Treating

produced water concentrate (that has already

been lime treated) with sodium carbonate

precipitates calcium, strontium, barium, and

radium as the corresponding carbonates.

Because BaCO 3 is about twice as soluble as

SrCO 3 and slightly more soluble than CaCO 3 , it

is necessary to add sufficient carbonate to

precipitate all the Group II metals in order to

precipitate all of the barium. For the design

case produced water composition, Table 5

shows that the amount of sludge generated by

this process is almost a factor of four greater

than the amount generated by the sulfate

precipitation process. Table 4 shows the

composition of the wet carbonate sludge. The

226 Ra activity in this sludge exceeds the

regulation limit for disposal as nonhazardous

solid waste in Pennsylvania. Further, the

extractable barium concentration in the wet

sludge is much higher than is permissible

under TCLP. This sludge would need to be

dried and disposed of as NORM waste.IWC 12

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Table 5 shows the materials and

disposal cost for this process to be in the range

of $6.80

‐ 10.50/bbl raw produced water

($2.10/bbl for Na 2 CO 3 ; $4.70

‐ 8.40/bbl for

transportation and disposal of dry NORM

sludge). Although this process yields complete

softening of the produced water, the materials

and disposal costs are too high for this process

to be practical for pretreating Marcellus

produced water that has elevated levels of

barium and radium.

Table 4. Carbonate Sludge (design case)

Component Concentration in wet sludge a

Ca 122,000 ppm wt/wt

Sr 28,000 “ “

Ba 69, 000 “ “

226 Ra 56 pCi/gm

a carbonate sludge: 45 wt% solids

MODIFIED CARBONATE PRECIPITATION: In an

effort to minimize disposal costs for the

carbonate precipitation process, we considered

a modified process that yields nonhazardous

solid products and an aqueous concentrate of

BaCl 2 and RaCl 2 , which may be disposed of by

UIC. Figure 4 shows a process flow diagram for

this process, in which sodium hydroxide is

added to selectively precipitate calcium and

strontium as hydroxides, which are less soluble

than either barium hydroxide or radium

hydroxide. The solids from Precipitation Stage

1 are nonhazardous and may be disposed of in

a RCRA

‐ D nonhazardous landfill.

Figure 4. Modified Lime

‐ Soda Process In Precipitation Stage 2, the produced water is

treated with sodium carbonate to precipitate

both barium and radium as carbonates. The

Stage 2 carbonate precipitate is removed from

the produced water and treated with HCl to

convert BaCO 3 and RaCO 3 to BaCl 2 and RaCl 2 , respectively. Carbon dioxide is vented to the

atmosphere. HCl addition is adjusted to

achieve a pH low enough to strip essentially all

of the carbonates from the aqueous

concentrate stream (e.g. pH 2

‐ 4). This

concentrate stream may be neutralized if

desired prior to disposal by UIC.

After Precipitation Stage 2, the softened

produced water still contains a significant

concentration of dissolved carbonates (about

400

‐ 500 ppm/w CO 3 = for design case produced

water). HCl is added to this stream to drive off

CO 2

. The softened, decarbonated produced

water may then be thermally treated to recover

distilled water and a solid salt product.

As shown in Table 5, the combined costs

(materials and disposal) are too high for this

process to be economical for pretreatment of

produced water with high barium and radium

levels. However, if inexpensive sources of

NaOH, KOH, Na 2 CO 3 , and/or K 2 CO 3 are

available, this process may be viable,

particularly because the produced water is

essentially completely softened, which enables

high recovery of distilled water and clean salt.

We successfully demonstrated this

process in the lab. A stoichiometric amount of

NaOH, based on the amount of Mg, Ca, and Sr

in the initial sample, was added portionwise to

a beaker of Well

‐ 5 (Table 3) produced water.

The supernatant was sampled after each

aliquot for liquid scintillation counting to

measure the amount of radium remaining in

solution. Then a series of six portions of

Na 2 CO 3 was added in the same manner, with

sampling after each portion.

Figure 5 shows the results of this

experiment. Here, the radium remains in

solution throughout the course of the NaOH

addition. Only after all the Mg, Ca, and Sr haveIWC 12

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all precipitated does the radium begin to

precipitate.

In contrast, when we utilized Na 2 CO 3 in

the Stage 1 precipitation step, radium

precipitated nonselectively along with the

other Group II metals.

Figure 5. Modified Carbonate Process Results

SELECTIVE RADIUM ADSORPTION: We explored

several classes of adsorbents to selectively

remove radium from produced water, which

would enable barium to be subsequently

removed by conventional sulfate precipitation.

DOWEXTM RSC (radium

‐ specific complexer) has

been utilized to remove radium in municipal

water systems 12

. However, as previously

reported 13

, we found that the 226 Ra capacity of

RSC (and all other adsorbents screened) was far

too low to economically remove radium from

produced water.

MnO 2 ADSORPTION: MnO 2 is well

‐ known as an

effective adsorbent for both barium and radium from aqueous solutions 14

. We tested bulk

MnO 2 (Fluka activated MnO 2 obtained from

Fluka Corp.), proprietary MnO 2 adsorbents

from Pacific Northwest National Labs (PNNL),

and a series of adsorbents made internally at

GE Global Research. Table 5 shows the

materials and disposal costs for single

‐ use

adsorbents with radium capacities of 2,500 and

5,000 pCi/gm. To be commercially attractive,

the materials and disposal cost for MnO 2 adsorption needs to be lower than the cost of

sulfate precipitation. Therefore, we set the

target radium capacity at 5,000 pCi/gm. We

utilized a “best case” produced water for these

screening tests, which has relatively low TDS

(68,000 mg/L) and a very low barium

concentration (32 mg/L). Table 3 shows the

composition of this water, which is designated

as “Well

‐ 4”. The low TDS and low barium

concentration enabled significant 226 Ra capacity

for all adsorbents tested, and enabled the use

of liquid scintillation counting for capacity

measurements. The 226 Ra capacity for bulk

MnO 2 was approximately 140 pCi/gm. The

capacities for 7 of the 14 PNNL MnO 2 samples

were in the range of 2000

‐ 2600 pCi/gm. These

capacities are too low to be commercially

viable. We demonstrated a 226 Ra capacity in

excess of 5,000 pCi/gm on a laboratory scale

with adsorbents developed internally at GE

Global Research, using Well

‐ 4 produced water.

Further development is in progress to validate

these adsorbents at a pre

‐ pilot scale for a range

of produced waters (e.g. design case) and

evaporator concentrates.

Table 5. Ba, Ra Removal Pretreatment Options and Costs for Design Case Produced Water

Process lb dry sludge

bbl PW Materials

$/bbl a Disposal $/bbl a Materials +

Disposal $/bbl a

Chelating ion exchange

‐ $4.75 $1.55 b $6.30

Nanofiltration

‐  ‐ $7.70 b $7.70

Sulfate coprecipitation 3.69 $0.15 $1.05

‐ $1.85 c $1.20

‐ 2.00

Carbonate precipitation 14.07 $2.10 $4.70

‐ $8.40 c $6.80

‐ 10.50

Modified carbonate precipitation 8.23 $2.95 $0.75 b $3.70

Selective Ra adsorption

‐  ‐  ‐  ‐IWC 12

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MnO 2 adsorption (5,000 pCi/gm) 0.35 $1.05 $0.10

‐ $0.20 $1.15

‐ $1.25

MnO 2 adsorption (2,500 pCi/gm) 0.35 $2.10 $0.20

‐ $0.40 $2.30

‐ $2.50

a materials and disposal cost per bbl raw produced water (design case composition)

b includes transportation cost from central PA and UIC disposal in OH

c includes transportation cost from central PA to TX and disposal in NORM disposal facility

SUMMARY AND CONCLUSIONS

Much Marcellus shale gas produced water has

elevated levels of TDS, barium, and NORM

( 226 Ra). Economical methods for recovery of

distilled water and a salable salt product from

Marcellus shale gas produced water are

necessary for continued development of this

resource. Current evaporator technology

(mobile or fixed) enables approximately 56%

water recovery as distilled water and yields an

aqueous concentrate that can be either

disposed of by UIC or further evaporated in a

central crystallization plant to recover

additional distilled water and a solid salt

product. In order to generate a solid salt

product that is safe to use as road salt, it is

proposed to remove radium and barium from

the evaporator concentrate prior to

crystallization.

We evaluated 7 processes for barium

and radium removal from evaporator

concentrate, based on a design case produced

water composition. The materials and disposal

costs for each process were estimated based on

a material balance. A key need for each

process is a means of disposing of a

concentrate of barium and radium, either as an

aqueous stream or as a solid. Aqueous

concentrates may be disposed of by UIC in

Ohio; solid NORM concentrates may be

transported to Texas for disposal at a NORM

waste disposal facility.

Of the processes evaluated, the lowest

cost options for the design case produced

water composition are sulfate precipitation and

adsorption on MnO 2

. Sulfate precipitation is a

well

‐ known process that yields (Ba,Ra)SO 4 , which is stable. MnO 2 adsorption has the

potential to operate at a lower cost, but further development is needed before this process can

be commercialized.

ACKNOWLEDGEMENTS

Funding for this project is provided by

RPSEA through the “Ultra

‐ Deepwater and

Unconventional Natural Gas and Other

Petroleum Resources” program authorized by

the U.S. Energy Policy Act of 2005. RPSEA

( www.rpsea.org ) is a nonprofit corporation

whose mission is to provide a stewardship role

in ensuring the focused research, development

and deployment of safe and environmentally

responsible technology that can effectively

deliver hydrocarbons from domestic resources

to the citizens of the United States. RPSEA,

operating as a consortium of premier U.S.

energy research universities, industry, and

independent research organizations, manages

the program under a contract with the U.S.

Department of Energy’s National Energy

Technology Laboratory.

The authors would like to acknowledge

the technical discussions between themselves

and Robert L. Solomon and Carolina Gonzalez,

both with GE Power and Water/RCC.

DOWEX RSC  Registered Trademark of

The Dow Chemical Company (“Dow”) or an

affiliated company of Dow.IWC 12

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REFERENCES:

1 PA DEP Website for Marcellus shale gas waste

generation and disposal:

https://www.paoilandgasreport ing.state.pa.us/publicrep

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and Gas Journal, Vol. 97, Jan 4, 1999, pp. 37

‐ 43.

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9 http://www.gewater.com/winflows.jsp

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‐ 10

‐ 65, San Antonio, TX, October,

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‐ 675

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‐ 07, Orlando, FL, November, 2011.

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