Technical Requirements 4.1 Appearance: It is a brown to brown homogeneous liquid with no obvious suspended matter and sedimentation. 4.2 Physical and chemical indicators The physical and chemical indicators should meet the requirements of Table 1. Table 1 Physical and chemical index project indicators pH value range 3.0-9.0 Mass concentration of organic matter, g/L ≥ 50.0 Weight concentration of total trace elements (Fe+Zn), g/L ≥ 100.0 Mass fraction of water-insoluble substances a, % ≤ 10.0 Mercury (Hg) content, mg/kg ＜ 0.05 Arsenic (As) content, mg/kg ＜ 1.3 Cadmium (Cd) content, mg/kg ＜ 0.5 Lead (Pb) content, mg/kg ＜ 5.0 Chromium (Cr) content, mg/kg < 2.0 a The total mass fraction of trace elements refers to the mass fraction of at least one of the two elements zinc and iron. The content of a single element less than 0.1g/L is not counted.