S1

SUPPLEMENTARY MATERIAL

Colloidal Behavior of Goethite Nanoparticles Modified with Humic

Acid and Implications for Aquifer Reclamation

Journal of Nanoparticle Research

Alberto Tiraferri, Laura Andrea Saldarriaga Hernandez, Carlo Bianco, Tiziana Tosco,

Rajandrea Sethi*

DIATI (Department of Land, Environment and Infrastructure Engineering)

Politecnico di Torino

C.so Duca degli Abruzzi 24, Torino 10129, Italy

Corresponding Author: Tel +39-011-090-7735; Fax: +39-011-090-7699; e-mail: rajandrea.sethi@polito.it

This Supplementary Material file is 11 pages long and it contains 7 figures and 3 tables.

Table of Contents

Figure S1. Electrophoretic mobility of humic acid-coated goethite nanoparticle suspensions as a function of

ionic strength in (a) NaCl, (b) CaCl2, and (c) MgCl2. ...................................................................................... S2

Figure S2. Examples of raw data from aggregation experiments. ................................................................... S3

Figure S3. Apparent aggregation rate as a function of slurry concentration in the presence of 0.7 mM CaCl2.

.......................................................................................................................................................................... S4

Figure S4. Representative results of sedimentation experiments. ................................................................... S5

Table S1. Pictures of sedimentation vials for different doses of calcium. ....................................................... S6

Figure S5. Representative results of sedimentation experiments of suspensions from which most of the

unadsorbed humic acid were removed by filtration. ........................................................................................ S7

Figure S6. Breakthrough curves of humic acid-coated goethite nanoparticles (total solid content of 1.70 g/L)

in silica sand in 10 mM NaCl. .......................................................................................................................... S8

Figure S7. Pictures of the column during transport tests carried out in 1.5 mM CaCl2 and 10.2 g/L solid

content. ............................................................................................................................................................. S9

Table S2. Pictures of sedimentation vials for different dilutions in tap water. .............................................. S10

Table S3. Results of transport tests conducted with suspensions diluted with tap water. ............................. S11

S2

Figure S1. Electrophoretic mobility of humic acid-coated goethite nanoparticle suspensions as a function of

ionic strength in (a) NaCl, (b) CaCl2, and (c) MgCl2. Mobilities were measured at varying slurry

concentrations. Data points are averages of at least three runs; lines are intended to be used as guide for the

eyes only. Experiments were performed at pH 7.5-8 and at 25°C.

S3

Figure S2. Examples of raw data from aggregation experiments. Change of hydrodynamic diameter

measured in time for (a) a suspension of 440 mg/L solid content upon addition of 140 mM NaCl, (b) a

suspension of 220 mg/L solid content upon addition of 300 mM NaCl, (c) a suspension of 440 mg/L solid

content upon addition of 300 mM NaCl, (d) a suspension of 110 mg/L solid content upon addition of 1050

mM NaCl. NaCl was added at time zero. Best linear fit of the initial increase in diameter is shown and the

value of its slope is indicated in red. Experiments were conducted at 25°C and at a pH value of 7.5.

S4

0.0 0.2 0.4 0.6 0.8 1.0

5x10-4

10-3

1.5x10-3

2x10-3

2.5x10-3

3x10-3

0.7 mM CaCl2

no

rma

lized

ap

pa

rent

ag

gre

gation

ra

te

(g/L

)-1(1

/s)

solid concentration (g/L)

44.8 mM NaCl

4x10-7 (g/L)

-1(1/s)

Figure S3. Apparent aggregation rate as a function of slurry concentration in the presence of 0.7 mM CaCl2.

The normalized rate, independent of solid concentration, that would be observed in 44.8 mM NaCl is

equivalent to 4×10‒7

(g/L)‒1

(1/s) and is three order of magnitude lower than the lowest rate measured with

calcium at the largest solid concentration probed in this study. Experiments were conducted at 25°C and at a

pH value of 7.5-8.

S5

Figure S4. Representative results of sedimentation experiments. Normalized light absorbance of samples at

800 nm wavelength for (a) a solid content of 1.02 g/L and varying concentration of CaCl2, (b) a solid content

of 2.55 g/L and varying concentration of CaCl2, (c) a solid content of 1.70 g/L and varying concentration of

MgCl2. The different concentrations are labeled. Experiments were performed at pH 7.5-8 and at

temperature of 25 °C.

S6

Table S1. Pictures of sedimentation vials for different doses of calcium.

time 10.2 g/L 5.10 g/L 1.70 g/L

0

10 min

40 min

1.5 hr

3 hr

DI 0.5 1 1.5 2 2.5 mM CaCl2

S7

Figure S5. Representative results of sedimentation experiments of suspensions from which most of the

unadsorbed humic acid were removed by filtration. Normalized light absorbance of samples at 800 nm

wavelength for (a) a solid content of 1.02 g/L, (b) 1.70 g/L, and (c) 5.10 g/L and varying concentration of

CaCl2. The different concentrations are labeled. Experiments were performed at pH 7.5-8 and at

temperature of 25 °C.

S8

Figure S6. Breakthrough curves of humic acid-coated goethite nanoparticles (total solid content of 1.70 g/L)

in silica sand in 10 mM NaCl. The nanoparticle suspension was introduced at time 0. The key experimental

conditions were: pH 7.5-8, porosity 0.45, mean grain diameter 0.87 mm, pore volume 10.2 mL, temperature

25 °C, and approach velocity 1.7×10‒4

m/s.

S9

Figure S7. Pictures of the column during transport tests carried out in 1.5 mM CaCl2 and 10.2 g/L solid

content.

S10

Table S2. Pictures of sedimentation vials for different dilutions in tap water.

time 10x 20x 40x 60x

20 min

50 min

5 hr

24 hr

S11

Table S3. Results of transport tests conducted with suspensions diluted with tap water.

dilution comment

60x transport test was impossible; the suspension sedimented in < 1 hour

40x transport test was impossible; the suspension sedimented in < 1 hour

20x the suspension sedimented during injection and was fully sedimented at the end of the

transport test; test was possible as long as the suspension was stable but solids stayed

entrapped in the column after flushing; the average hydrodynamic diameter of the

nanoparticles at the end of the test was 1.59 μm.

Injection suspension at the end of the test

Column appearance during injection

Column appearance at the end of the test after flushing

10x the suspension was stable and the transport test was successful; the column appeared clean

after final flushing; the dimension of the particles in the injection tank was 126 nm at the end

of the test.