The chemical nature of arsenic depends mainly on its oxidized state, namely trivalent arsenic and pentavalent arsenic.
1. Trivalent arsenic As ³⁺ , the solid material is usually in the form of As ₂ O ₃ , and the liquid is present as the arsenide-arsenic acid cation. Crystalline salts are common sodium arsenite, silver arsenite and copper arsenite. The dissociation of arsenious acid is as follows:

2. Pentavalent arsenic As ⁵⁺ , as found in the form of As ₂ O ₅ . The pentavalent arsenic acid is crystallized into a tribasic acid and expressed by the 2AsO ₄ H ₃ •H ₂ O molecular formula.
Dissociation balance in solution:

Arsenic similar electronic structure and atomic radii phosphorus phase, and thus the chemical nature of these two elements is also very similar, especially positive pentavalent acid acidity almost the same, thereby taking advantage of these properties to improve the efficiency of removal of arsenic from water. Natural mineral mainly arsenic enargite (Cu ₃ AsS _4), or arsenic trisulfide said orpiment (As ₂ S _3), arsenic ore cobalt (Co AsS _2), said arsenic pyrite or arsenopyrite (FeAsS The minerals of these minerals are neutral and slightly soluble in water. When the useful symbiotic element gold is recovered by chemical treatment, it will be converted into a readily soluble arsenic compound. For example, in the process of recovering gold from sulfide ore, the ore is acidified and roasted, and the arsenic becomes a fine powdery arsenic oxide. It is dissolved in the liquid phase by gas phase and roasting ore and needs to be treated, otherwise it will pollute the environment. .

Cold mill intermediate rolls