Silicate Chemistry: Speciation

NSL Silicate Drilling Fluids Seminar

National Silicates Ltd.an affiliate of The PQ CorporationNational Silicates Ltd.an affiliate of The PQ Corporation

Acknowledgements

Dr. Jonathan Bass, PQ Corporation Dr. Neil Miller, PQ Corporation Rick Reifsnyder, PQ Corporation Dr. Gary Turner, Spectral Data Services, Inc.

Outline Technical Service Overview Soluble Silicates Manufacturing Important Physical Properties Basic Silicate Reactions Silicate Speciation Relevance to Silicate Product Selection and

Drilling Mud Formulation

NSL / PQ Development Projects

High Temperature Formulations Lubrication Technology Alternative Viscosifiers Mechanism(s) of Inhibition Overcoming Mud Contamination

National Silicates Ltd.an affiliate of The PQ CorporationNational Silicates Ltd.an affiliate of The PQ Corporation

Other End-Use Applications

Adhesives Binders Cements Detergency Foundry Feedstock

Grouting Paints / Coatings Pulp & Paper Water Treatment Waste Treatment Miscellaneous

Health, Safety and Environment

All silicates are simple, three component products– silica -- alkali -- water

One of the safest industrial chemicals No toxic or volatile material Stable for extended periods of time Mild reactivity Non-flammable

Soluble Silicates Soluble Silicates are the metal salts of

Silicic Acid that exist in multiple polymeric forms in solution. Amorphous solids and powders are also manufactured.

All silicates contain three basic components:– Silica -- SiO2 (Sand)

– Alkali -- Na2O or K2O (Soda Ash or Pot Carb)

– Water -- H2O

Silica ChemistrySolubility

Silicas are not dissolved by acids except

HF

Apparent increase in solubility above pH

9: formation of monomer and silicate ion

(SiO2)x + 2H2O = Si(OH) 4 + (SiO2)x-1

Si(OH)4 + OH- = SiO(OH)3- + H2O

Soluble Silicates

Water

SilicaAlkali1

4

2

5

3

1. High Alkali Granular2. Metasilicates3. Glasses4. Hydrous Powders5. Commercial Liquids

50%

Soluble Silicates Changing the proportions of silica, alkali

and water will control chemistry and physical properties.

All combinations are possible but many yield unstable, insoluble and undesirable products.

Manufacturing experience and expertise can produce optimum silica species for each end use.

Manufacturing Raw Materials:

– Silica Sand -- Source determines purity

– Sodium Carbonate or Potassium Carbonate

– Softened Water

Na2CO3 + xSiO2 = Na2O•xSiO2 + CO2

K2CO3 + xSiO2 = K2O•xSiO2 + CO2

Combined in open hearth furnace

Silica Tree

S an d

B rites ilG & G D

H yd ra tedS ilica tes

N yaco lP rod u c ts

E K A N ob e l

C o llo id a l S ilica(S ilica S o ls )

IM P A QB TR S ep ara tion s

D u p on t

B ritesorb

S ilica G e ls

Q u soG & W R S eries

D eg u ssa

P rec ip ita tedS ilicas

M etsoP rod u c ts

M etas ilica tes

V a lfo rP rod u c ts

Z eo litesS od iu m A lu m in o

S ilica tes

L iq u id S ilica tes

S ilica te G lass

F u rn ace1 1 0 0 to 1 2 0 0

d eg rees C

S od a A sh

Raw Materials Raw Materials

Heat Energy

Add Water

Product Properties & General Chemistry

Important Product Properties

Alkali Content Silica Content Total Solids Ratio

Density pH Viscosity Clarity & Purity

Alkali Content

TTA (Total Titratable Alkali)%Na2O or %K2O

Simple acid /base titration using a colored mixed indicator.

Combination of active and inactive alkali

Silica Content

Multiple analytical methods Gravimetric Silica Determination Volumetric Silica Titration Atomic Adsorption Spectroscopy Colorimetric determination Geriche Charts or the Silica Program.

( TTA and density in degrees Baume )

Total Solids

The combined total of the Silica & Alkali values.

Solubility and physical properties are affected by solids level.

As solids increase, there is a corresponding increase in viscosity for a particular ratio.

Ratio Ratio is the most important physical property

silicate variable. Weight ratio is defined by the following:

Weight % of silica divided by the Weight % of Alkali

Ratio determines:-- Solubility of solids & powders-- Reactivity of silicate-- Physical properties such as viscosity

Weight ratio and Molar ratio are nearly equivalent for sodium silicates but not for potassium silicates.

Density Of Silicates Typically measured at 20 degrees C using a hydrometer. The BAUME scale is ordinarily used. Easily convertible to specific gravity. Other density measuring methods

– Pycnometer ( Accurate but difficult )– Graduated Cylinder ( Easy but precision is limited )– Digital Density Meter ( Very accurate and easy to use, however

the equipment is expensive and must be thoroughly maintained )

The Baume scale is somewhat proportional to the solids content of the silicate being measured.

Density vs. Solids

Viscosity vs. Ratio and Solids

pH All silicate products are in the pH range from 11.0 to 13.5. pH is a function of:

– Silicate composition (ratio)– Solids concentration

The pH of silicates does not reflect the true alkali content of solutions.

General Trends:– pH of silicate solutions is maintained until almost complete

neutralization.– The buffering capacity of silicate solutions increases with

increasing proportions of soluble silica.

Basic Chemical Reactions

Four Basic Silicate Reactions

– Hydration / Dehydration

– Metal Ion Reactions

– Surface Charge Modification

– Polymerization / Gelation Reactions

Hydration/Dehydration The addition or removal of water from silicates:

– Soluble Silicates are unique in the way that the solid materials dissolve and the liquids dry.

– Rate of Solution as well as Rate of Drying depend greatly on product Ratio.

– The Glassy Nature of Silicates imparts strong and rigid physical properties to a dried film or coating.

– This property impacts handling procedures.

Metal Ion Reactions Soluble Silicates can react with all multivalent cationic metal ions to form

the corresponding insoluble metal silicate, depending on reaction conditions.

Examples: Calcium Manganese MagnesiumCadmium Iron Aluminum

Silicates can precipitate these metals out of solution and render them insoluble and non-reactive.

In moderately alkaline silicate drilling fluids, precipitation of insoluble metal silicates can be easily controlled

Reaction of silicates at shale surfaces are predominantly polymerization / gelation reactions resulting in the formation of hydrous, sodium - rich metal silicate gels.

Shale Stabilization Reaction with metal cations is basis of

functionality. Silica reacts with shale surfaces to form

semi-permeable gel. Also can gel in voids and small cracks. Gels can be removed with water / alkali if

desired ( e.g. payzone silicate breaker Limits fluid penetration. Stabilizes cuttings.

Hydrous Metal Silicate Gels

Effect of Contaminants

Metals and acidic materials will inactivate silica species.

Precipitation & Gelation. May impact fluid rheology and ability to

stabilize shale. Maintain adequate silica and alkali

reserves. Maintain pH value

Silicate Speciation

Silicate Speciation

Definition and use of chemical features to provide performance benefits

Identify species control Control and optimize species change

Silicates: Unit Chemical Structures

O

O

SiO

O

OSi

OSi

OSi

O

O

O

O

O

O

O

Monomer, Q = 0 Trimer, Q = 1.3

Cyclic trimer, Q = 2.0

Cyclictetramer, Q=2.0

Cubic octamer, Q=3.0

29Si NMR of Silicates - Band Assignment

-60 -70 -80 -90 -100 -110

ppm

Q0

O

O

SiO

O

Q1

OSi

OSi

OSi

O

O

O

O

O

O

O

Q2cyt

Q2

Q3

Q4

2 ratio, 3M

29Si NMR of Silicates - Effect of Ratio

-70 -80 -90 -100 -110 ppm -60 -70 -80 -90 -100 -110 ppm

3.2 Ratio, 6M 2.0 Ratio, 6M

29Si NMR of Silicates - Effect of Concentration

3.2 Ratio, 6M 3.2 Ratio, 1M

29Si NMR of Silicates - Effect of Concentration

2.0 Ratio, 6M 2.0 Ratio, 1M

0

10

20

30

40

50

60

70

80

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Ratio

Apparent

Relative

Concentratio

n

Monosilicate Chains & Cyc Trimers Larger Rings Complex Structures

Figure 2

Qualitative Interpretation ofSilicate Anion Structure Equilibria - 1 Molar Solution

Spec PQ CORPORATION

Speciation: A Current View

SiO44- Dimer Planar Cubic Polymer

Trimer Cyclics Octamer

SiO2

Charge

Alkali+ -- ++ -

Viscosity+ +

Concentration Effects on Speciation

Decreasing concentration depolymerizes silicate anions and is more pronounced for lower ratio silicates

For 2.07 ratio, in the range 6M to 1M SiO2, Q2

4R and Q33R decrease, bicyclic

anions are relatively stable, Q1 and Q23R

increase and Q0 (monomer) increases For 3.2 ratio, from 6M to 1M SiO2, the

larger cyclic anions are relative stable, while dimers and monomer increase.

Influence of Metals on Silicate Speciation

The common metal impurities sum to ~250 ppm on a liquid silicate basis

Metal ions such as Al, Fe, Ti are network formers but at ppm levels do not affect overall distributions as visible by NMR; these metals are incorporated into the larger anions

Calcium (and magnesium to a lesser degree) does not influence AMW vs. ratio, but does promote turbidity formation especially at higher ratio (Q3 and Q4)

Influence of Temperature on Speciation

In general, temperature increases in the range RT to 200 oF promote depolymerization in silicates

1.6 ratio silicate shows increases in monomer and Q1 with decreases in large cyclics and smaller 3-D oligomers

3.2 ratio silicate shows increases in monomer and Q1 and decreases in large oligomers (Q3) and polymer (Q4) with temperature increase

Influence of Additives on Speciation

Additives influence speciation differently depending on additive type, concentration, and silicate ratio

As an example, 10% NaCl appears to stabilize Q2 and Q3 in lower ratios and Q4 in higher ratios when temperature is increased

Excessive additive concentration can interact with large oligomers and polymer in silicates to yield precipitates and gelation, e.g., 3.2 ratio, high salt, high calcium.

Effect of RevDust on Speciation

RevDust added at 8, 17, 25 ppb to 2 ratio, 7% solids, 22% NaCl

Ratio increased 2 to 2.4 (alkali decrease) with RevDust loading

Large anions and polymer appear as RevDust loading increases, viscosity can increase, ultimate gel formation with addt’l ratio increase

Effects above increase with temperature Effects follow from alkali depletion

Summary 2.00 ratio provides the best overall

balance between mud stability and inhibitive performance

Higher silicate concentration complements performance and provides resistance to contamination

Judicious selection of mud additives is crucial and will greatly affect performance