Supplementary material

Supplementary material

A two-step pH control method to remove divalent metals from near-neutral mining and metallurgical waste drainages by inducing the formation of layered double hydroxide

Franco Frau ^a,* , Roberta Atzori ^a , Carla Ardau ^a , Daniela Medas ^a , Francesca Podda ^a , Elisabetta Dore ^a , Alfredo Idini ^a , Gioacchino Tempesta ^b , Giovanna Agrosì ^b

a

Department of Chemical and Geological Sciences, University of Cagliari, Cagliari, Italy

b

Department of Earth and Geoenvironmental Sciences, University of Bari, Bari, Italy

* Corresponding author: frauf@unica.it

1

Fig. S1. Aerial view of the “Red Muds” deposit (from Google Earth, modified).

2

a b

c d

Fig. S2. a) Partial view of the “Red Muds” deposit. b) and c) Sampling points of the drainage water. d) White, soluble

efflorescences at the sampling point mainly consisting of gypsum and Zn-sulphates.

Table S1. Chemical composition of the "Red Muds" drainage water determined before and after different metal removal experiments.

Ca Mg Na K SO

Zn Mn Cd Pb Ni

mg/L mg/L mg/L mg/L mg/L mg/L μg/L μg/L μg/L μg/L

before 440 630 91 110 4000 205 1800 1400 97 60

Exp-1

after 420 617 701 109 4307 1.20 247 878 6.47 0.73

%

variation -4.55 -2.06 670 -0.91 7.68 -99.4 -86.3 -37.3 -93.3 -98.8

Exp-2

after 390 604 436 110 4133 77 1020 1387 35 7.22

%

variation -11.4 -4.13 379 0.00 3.33 -62.5 -43.3 -0.93 -63.9 -88.0

Exp-3

after 435 610 399 108 4215 2.11 972 937 4.05 1.85

%

variation -1.14 -3.17 338 -1.82 5.38 -99.0 -46.0 -33.1 -95.8 -96.9

Exp-4

after 412 626 91 109 4164 203 1800 1355 97 60

%

variation -6.36 -0.63 0.00 -0.91 4.10 -0.98 0.00 -3.21 0.00 0.00

Exp-5

after 389 602 789 107 4195 0.55 38 835 7.80 1.12

%

variation -11.6 -4.44 767 -2.73 4.88 -99.7 -97.9 -40.4 -92.0 -98.1

Table S2. Fit parameters for EXAFS analysis of the precipitates at pH 4.2, pH 6 and pH 8.5, and of the reference compound ZnAl LDH. The number in brackets indicates the uncertainty on the last digit of the refined parameters.

ZnO ZnAl ZnZn

Sample CN R 

CN R 

CN R 

R

Å x10

Å

Å x10

Å

Å x10

Å

pH 4.2 4.1(4) 1.97(5) 9.2(7) 1.0(1) 3.09(9) 4.3(9) 0.05

pH 6 6* 2.06(2) 16(1) 0.5 3.07(5) 11(1) 0.8 3.15(3) 11(1) 0.1

pH 8.5 6* 2.06(2) 0.8 3.07(5) 11(1) 1.2 3.14(3) 11(1) 0.1

ZnAl LDH 6* 2.09(2) 8.0(4) 1.8 3.06(5) 12(1) 2.7 3.10(2) 12(1) 0.09

CN = Coordination Number; R = interatomic distance; σ

=Debye-Waller factor; R

= best fit factor; (*) means fixed

coordination numbers, constrained accordingly to crystallographic model.