| Metallic ion in untreated dye solution | Final concentration of metal in treated solution (ppm) |
% reduction of metallic content in solution |
Absorbance and appearance of treated solutions |
Extended treatment (the “polishing” step) |
|---|---|---|---|---|
| Ni2+ | 0.053 | 98.9% | 1. Clear, colourless liquid. 2. Absorbance = 0.025 3. Black ppt. likely to be Ni.O(OH) |
Not needed. |
| Co2+ | 0.048 | 99.0% | 1. Clear, colourless liquid. 2. Absorbance = 0.024 3. Black ppt. likely to be Co.O(OH) |
Not needed. |
| Fe2+ | 0.039 | 99.1% | 1. Clear, colourless liquid. 2. Absorbance = 0.022 3. Deep orange ppt. likely to be “Fe(OH)3” |
Not needed. |
| Cu2+ | 0.55 | 89.6% | 1. Light tint of peach colouration. 2. Absorbance = 0.036 after extended treatment. 3. Black CuO ppt. |
Activated charcoal removed the peach tint to give a clear colourless liquid. Ion-exchange removed Cu2+ ions further after acidification. |
| Cr3+ | 1.50 | 65.3% reduction from a 10-fold diluted dye solution | 1. Light yellow tint. 2. Absorbance = 0.047 after extended treatment. 3. No ppt. formed during the entire course of treatment. |
Activated charcoal reduced the vestigial yellow tint further, followed by a reduction of Cr(VI) to Cr(III) with thiosulphate, resulting in colourless water; ion exchange then reduced Cr3+ concentration. |