sample ID

purification protocol

Colour of diatom solution

Organic residue after purification (ATR)

Morphology (SEM)

D0 (reference)

heating at 100˚C

brown

Yes

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D1

1 step 80 mL HNO₃

brown

Yes

------

D2

1 step 80 mL HNO₃ + 1 step 160 mL HNO₃

White-yellow

No

------

D3

1 step 160 mL HNO₃ at 65˚C

green

No

------

D4

1 step 160 mL HNO₃ at 65˚C + calcination at 300˚C for 2 h

White-yellow

No

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D5

1 step 160 mL HNO₃ at 0˚C

White-yellow

No

smashed

D6

1 step 160 mL HNO₃ at 0˚C ungrounded

White-yellow

No

entire

D7

1 step 160 mL HNO₃ at 0˚C ungrounded + calcination at 300˚C

White-yellow

No

------

D8

1 step 40 mL ammoniac (T_amb)

Green-brown

Yes

------

D9

1 step 40 mL HNO₃ at 50˚C

Yellow

No

------

D10

1 step 20 mL HNO₃ at 0˚C + 20 mL acetone (T_amb)

Brown

Yes

------

D11

1 step 20 mL HNO₃ at 0˚C + 20 mL ammoniac at 35˚C

Yellow

No

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D12

1 step 20 mL HNO₃ at 0˚C + 20 mL ammoniac at 0˚C

White-Yellow

No

Entire

D12 scale-up

1 step 200 mL HNO₃ at 0˚C + 200 mL ammoniac at 0˚C

White

No

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D13

IFREMER sample HNO₃

Yellow/white

No

Entire