Cacl2

L-lactic acid (A.R., 90%) was purchased from Musashino Chemical (Yichun, China) Corporation. Ethylenediamine (A.R.), hydrochloric acid (A.R.), NaOH (A.R.), FeCl₃ (A.R.), FeCl₂·4H₂O (A.R.), CuCl₂·2H₂O (A.R.), MgCl₂·6H₂O (A.R.), NiCl₂·6H₂O (A.R.), CaCl₂ (A.R.), SnCl₂ (A.R.), KCl (A.R.), CoCl₂·6H₂O (A.R.), and LiCl·2H₂O (A.R.) were all bought from Nanjing Chemical Reagent Company (Nanjing, China). A dialysis bag with a molecular weight cut-off of 1000 Da was purchased from Shanghai Yuanye Bio-Technology Co., Ltd (Shanghai, China). The deionized water was purified using an Ulupure system (Nanjing Youpu Environmental Protection Equipment Co., Ltd, Nanjing, China) throughout all the experiments. All reagents used were available commercially and did not involve purification.

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.