SELECTIVE SALT

RECOVERY FROM REVERSE

OSMOSIS BRINE USING

INTER-STAGE ION

EXCHANGE

Joshua E. Goldman

PhD Candidate

University of New

Mexico

Kerry J. Howe

Associate Professor

University of New

Mexico

Bruce M. Thomson

Regents Professor

University of New

Mexico

ACKNOWLEDGMENTS

• WateReuse

• CDM

• Purolite

• ResinTech

• Kerry Howe

• Bruce Thomson

• Mehdi Ali

• Steve Cabannis

• Angela Montoya

• Lana Mitchell

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PRESENTATION

OUTLINE

• Background

• Project Overview

• Bench Test Conclusions

• Pilot Testing Objectives

• Pilot Testing Results

• Conclusions

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CONCENTRATE

PRODUCTION

Concentrate disposal is a big problem in inland areas

• Expensive

• Complicated state and EPA regulations depending on

constituents in water

Brackish

Well

Concentrate

(Typically 10%-30%)

Fresh Water

(Typically 70%-90%)

RO

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CONCENTRATE

REDUCTION

Inter-stage sequential ion exchange

• Remove ions that form sparingly soluble salts from

concentrate

• Calcium, magnesium, sulfate

• Replace them with sodium and chloride

• 2nd RO stage to treat sodium chloride solution without

worrying about scaling

• 2nd stage RO concentrate used a regeneration solution for

cation and anion exchange columns

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SALT RECOVERY

• Calcium carbonate

• Pulp and paper

• Building construction (marble floors, roof materials, and roads)

• Glass (improves chemical durability)

• Rubber and plastic

• Paint (extend resin and polymers and control texture)

• Dietary supplement (antacids)

• Water treatment (pH control, softening)

• Calcium sulfate

• Drywall

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PROPOSED PROCESS TRAIN

Reverse

Osmosis

Stage 1

Stage 1

Permeate

Concentrate

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PROPOSED PROCESS TRAIN

Reverse

Osmosis

Stage 1

Stage 1

Permeate

Concentrate

Cation

Exchange

Anion

Exchange

Ca Mg CO3 SO4

Na CO3 SO4

Na Cl

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PROPOSED PROCESS TRAIN

Reverse

Osmosis

Stage 1

Stage 1

Permeate

Concentrate

Cation

Exchange

Anion

Exchange

Reverse

Osmosis

Stage 2 Stage 2

Permeate

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PROPOSED PROCESS TRAIN

Reverse

Osmosis

Stage 1

Brine

Reservoir

Stage 1

Permeate

Concentrate

Waste

Regeneration

Cation

Exchange

Anion

Exchange

Reverse

Osmosis

Stage 2 Stage 2

Permeate

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PROPOSED PROCESS TRAIN

Reverse

Osmosis

Stage 1

Brine

Reservoir

Precipitation

Basin

Stage 1

Permeate

Concentrate

Regeneration

Cation

Exchange

Anion

Exchange

Reverse

Osmosis

Stage 2 Stage 2

Permeate

Reverse

Osmosis

Stage 1

Brine

Reservoir

Stage 1

Permeate

Concentrate

Waste

Regeneration

Cation

Exchange

Anion

Exchange

Reverse

Osmosis

Stage 2 Stage 2

Permeate

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PILOT TESTING

OBJECTIVES

• Determine the consistency of the mass and purity of the

recovered salt products.

• Determine the “best” fraction of the regenerant solution to

use for salt recovery.

• Optimize the operation cycle length to maximize ion

concentrations in regeneration solutions and minimize

unused cation exchange capacity.

• Determine if pilot effluent recycle affects the performance

of the 2nd stage RO system.

• Determine the effect of anti-scalant addition on the resin

capacity.

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PILOT SCALE

TESTING

• Outside of Brighton, CO

• In conjunction with CDM

• June 6th – July 14th

• Continuous operation

Average Pilot Feed

RO Concentrate

mg/L

Ca 456

Mg 191

K 17

Na 570

Cl 613

SO4 957

TDS 4450

M

CO3 0.274

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PILOT SCALE

TESTING

Service Cycle 1-4 20 BV

Service Cycle 5-6 28 BV

Service Flow Rate 10 BV/hr

Regeneration Cycle 0.75 BV

Rinse Cycle 1 BV

Rinse and

Regeneration Flow

Rate

2 BV/hr

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15 of 38

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MASS ANALYSIS AND

QUANTIFICATION METHODS

• Tare Erlenmeyer flask

• Mixed 100 mL of each regeneration solution in

flask

• For low pH prepetition, adjust pH of anion

regeneration solution to 4

• Allow precipitates to form and settle for 36

hours.

• Separate liquid and solid by centrifuge

• Dry in the lab oven at 104°C for 24 hours

• Mass of flask - tared mass = precipitate mass

• Analyze precipitated solid by SEM, EDS, XRD

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VISUAL MINTEQ

MODELING

1 M Ca

1 M SO4

1 M CO3

-6

-5

-4

-3

-2

-1

0

1

2

3

4

0 2 4 6 8

pH

Saturation Index

Calcite

Gypsum

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PURE CALCIUM

CARBONATE

0

10

20

30

40

50

60

70

C O Ca

% C

om

po

sit

ion

(A

tom

ic)

0

10

20

30

40

50

60

70

C O Na Mg P S Cl Ca Sr

% C

om

po

sit

ion

(A

tom

ic)

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PURE CALCIUM

SULFATE

0

20

40

60

80

O Na Mg Si S Cl Ca

1

1

0

20

40

60

80

O Na Mg P S Cl Ca Sr

2

2

0

10

20

30

40

50

60

70

O S Ca

% C

om

po

sit

ion

(A

tom

ic)

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MASS ANALYSIS

RESULTS

Ambient pH Low pH

Representative

Sample

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MASS ANALYSIS

RESULTS - XRD

• Spectra Identified as CaCO3

• Ambient pH precipitate from Weeks 2-4

• Spectra Identified as CaSO4

• Low pH precipitate from Weeks 3,4,6

• Ambient pH precipitate from Week 6

• Other Spectra Identified

• Halite (NaCl)

• Week 2 Ambient pH

• Week 4 Low pH

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CONCLUSIONS FROM

MASS ANALYSIS

• Calcium sulfate and calcium carbonate can be precipitated

separately

• Low pH mixing conditions - calcium sulfate

• Ambient pH mixing conditions – calcium carbonate

• Except for Week 6

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MASS QUANTIFICATION RESULTS

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Week 1 Week 2 Week 3 Week 4 Week 5 Week 6

kg

Pre

cip

ita

te p

er

m3

RO

Co

nc

en

tra

te

Ambient pH

Low pH

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MASS QUANTIFICATION

CONCLUSIONS

• Salts precipitate spontaneously when the regeneration

solutions are mixed

• Possible to precipitate approximately 12 kg of gypsum per

cubic meter of regeneration solution

• Approximately 45% of the calcium is recovered

• Approximately 28% of the sulfate is recovered

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METHOD TO DETERMINE

BEST PORTION OF

REGENERATION SOLUTION

• Regeneration and rinse cycles total 1.75 BV

• Results from column tests showed sharp regeneration

curves

• Effluent samples taken every 5 minutes (0.17 BV)

• Anion column - conductivity and total carbonate

• Cation column - conductivity and calcium

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.00 1.00 2.00 3.00

Co

nc

en

tra

tio

n

(C/C

max)

BV 26 of 38

PILOT ELUTION

CURVES

0

0.2

0.4

0.6

0.8

1

1.2

0.0 0.5 1.0 1.5 2.0

C/C

ma

x

Bed Volumes

Conductivity TotCO3

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2

C/C

ma

x

Bed Volumes

Conductivity Ca

SBA SAC

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RESULTS – ION CONCENTRATION

AND SALT YIELD

Ca Mg SO4 NO3 CO3

Week mg/L mg/L mg/L mg/L M

5 5798 1708 17673 799 0.13

6 12546 3703 48167 1023 0.25

CF 2.2 2.2 2.7 1.3 1.9

• Significant increase in ion

concentrations

• 5.8x increase in salt yield

per unit treated RO

concentrate

• Increased total recovery of

total Ca and SO4 in system

from 5% to 20%

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Week 5 Week 6

kg

Pre

cip

ita

te p

er

m3

RO

Co

nc

en

tra

te

Ambient

Low

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OPTIMIZATION OF

OPERATION CYCLE

• Constructed breakthrough curve

• Started at end of standard operation cycle (20 BV)

• Grabbed samples of SBA and SAC effluent

• Sample taken every 2 BV (12 minutes)

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BREAKTHROUGH

CURVE

• Started taking samples at end of standard regeneration and rinse cycle

• Extended cycle to point just before magnesium breakthrough (28 BV)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

20 25 30 35 40

C/C

in

Bed Volumes

CO3 Ca Mg SO4

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OPTIMIZED

OPERATION CYCLE

Ca Mg NO3 SO4 CO3

mg/L mg/L mg/L mg/L M

Week 2 5096 1919 1090 10236 0.20

Week 5 5798 1708 799 17673 0.13

Increase

in Ratio

Ca:Mg 1.3x

SO4:CO3 2.7x

SO4:NO3 2.4x

0

5

10

15

20

25

Ca:Mg SO4:CO3 SO4:NO3

Re

sin

Ph

as

e Io

nic

Ra

tio

Week 2

Week 5

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OVERALL

CONCLUSIONS

• Separation factors can be predicted based on solution

characteristics

0

10

20

30

40

50

60

0 10 20 30 40 50 60

Pre

dic

ted

α C

a/N

a

Measured α Ca/Na

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OVERALL

CONCLUSIONS

• Column performance well predicted by separation factor

regressions and modeling

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40

Ca

lcu

late

d N

um

be

r o

f B

V t

o

Bre

ak

thro

ug

h

Measured Number of BV to Breakthrough

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OVERALL

CONCLUSIONS

• Gypsum can be spontaneously precipitated from mixed

cation and anion regeneration solutions

• Lab and pilot tests

• Requires pH adjustment when system not optimized for

sulfate recovery

• Can recover 45% of calcium and 28% of sulfate from the

mixed solution

• 15% of total possible gypsum recovered from RO

concentrate stream

• For a 5 MGD plant

• 6 tons/day of gypsum could be recovered

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OVERALL

CONCLUSIONS

• Process has potential to improve RO recovery and to

generate to gypsum

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QUESTIONS???

38 of 38