Sodium lignosulphonate

Sodium lignosulphonate, ferrous sulfate heptahydrate, sodium sulfite anhydrous, sodium hydroxide, and ethanol absolute were all in reagent grade and purchased from Shanghai Macklin Biochemical Co., Ltd., China.
Different specifications of plexiglass ion-exchange columns were ordered from Zhengzhou Glass Factory, China. The column with a diameter of 50 mm and a length of 500 mm was used for a lab-scale experiment, and the column with a diameter of 300 mm and a length of 1500 mm was used for a pilot-scale experiment. The centrifugal pump, peristaltic pump, and flowmeter were purchased from Jiangsu Pump Industry, Co., Ltd. Taizhou, China. The normal window gauze, bought from a local grocery store, was applied as the supporting material. The de-ionized water was used for dilution, and 1 M of HCl or NaOH was used for adjusting the pH of the solution.
The gold-smelting wastewater after the original treatment process of flocculation and precipitation using mainly lime, was from a local company smelting precious metals such as gold and copper. Table 1 shows the chemical composition of the wastewater during the period of observation. In view of the potentially toxic substances, during the process of handling the wastewater, CAUTION in the Supplementary Materials must be obeyed.

A variety of metal salts, including AgNO₃, Ni(NO₃)₂, BaCl₂, ZnCl₂, CuCl₂, CaCl₂, KOH, NaCl, AlCl₃, FeCl₂, MgCl₂, FeCl₃, MnCl₂, PbCl₂, HgCl₂, Co(NO₃)₂, and NaBH₄ were purchased from Nanjing Chemical Reagent Co., Ltd. (Nanjing, China). Sodium lignosulphonate was obtained from Macklin Biochemical Technology Co., Ltd. (Shanghai, China). All the chemicals were analytical grade and used without further purification. All aqueous solutions were made using deionized water.