Absolute ethanol

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.

The natural diatomite (denoted as D) used in this work is from Linjiang city, Jilin province, China [25 (link)]. The reagents used in this work are all purchased from Shanghai Macklin Biochemical Co., Ltd (Shanghai, China), including acetic acid (CH ${}_3$ COOH, AR), ethanol absolute (C ${}_2$ H ${}_5$ OH, AR), tetrabutyl titanate (C ${}_{16}$ H ${}_{36}$ O ${}_4$ Ti, donated as TBOT, AR), tert-butanol (C ${}_4$ H ${}_{10}$ O, donated as t-BuOH, AR), ethylenediaminetetraacetic acid disodium (C ${}_{10}$ H ${}_{14}$ N ${}_2$ Na ${}_2$ O ${}_8$ , donated as EDTA-2Na, AR), hydrochloric acid (HCl, AR), silver nitrate (AgNO ${}_3$ , AR) and zirconium oxychloride octahydrate (ZrOCl ${}_2$ ·8H ${}_2$ O, AR). Deionized water (≥10.0 M $\Omega$ cm) was used throughout our experiments.

All the chemicals used were analytical grade and were used without further purification: Sodium 4-methylbenzenesulfonate (GUANGFU, Tianjin, China, 98%), Cobalt hexahydrate chloride (VETEC, Speyer, Germany, 99%), Trisodium citrate (FUNCHEN, Tianjin, China, 99%), Potassium ferricyanide (BEILIANJINGXI, Tianjin, China, 99.5%), Sodium molybdate dihydrate (Boddi, Tianjin, China, 99%), Thiourea (ALADDIN, Shanghai, China, 99%), Pyrrole (MACKLIN, Shanghai, China, 99%), Ethanol absolute (MACKLIN, Shanghai, China, 95%).