## 3 Results
### Results of the Circulation Experiment  
In order to verify the feasibility of the whole process, the three processes were connected to carry out the circulation experiment. The process flow is shown in Figure 1. The cyanide-containing water was pumped into the chemical reaction tank, sulfuric acid was added to adjust the initial pH of the acidification reaction to 1.8, and after the full reaction, 0.1 g/L of sodium hydrosulfide was added for deep copper precipitation. After copper sinking, the solution was pumped into the plate and frame filter press through a pneumatic diaphragm pump, and the filter residue became copper products. The filtrate was further filtered through a precision filter, and the precision filter filtrate was pumped into the gaseous membrane module through an acid-resistant pump. During membrane treatment, the flow rate of cyanide-containing water was 0.3 m\({}^{3}\)/h, the flow rate of lye was 0.6 m\({}^{3}\)/h, and the number of membrane stages was two. After membrane treatment, cyanide-containing water was pumped as backwash water into the backwash tank of the countercurrent washing machine for backwashing the cyanide tailings. In the filter press backwash, the primary air-drying time was 1.5 min, the backwash water multiple was 0.7 times, and the secondary air-drying time was 10 min. The elution water after the filter press and backwashing was returned to the chemical treatment process for the circulation experiment, and the total cycle number was five. During the experiment, the leaching toxicity of the backwashed cyanide tailings was tested, and the elemental content analysis of the leached toxic solution (LTS), elution water, solution after acidification (SA), solution after vulcanization (SV), solution after primary membrane treatment (M1), solution after secondary membrane treatment (M2), and the lye after gaseous membrane treatment (ML) was carried out. The results of the circulation experiment are shown in Table 4.  
Figure 12: Effect of the flow rate of cyanide-containing water on the membrane treatment process. As we can see in Table 4, after chemical treatment and membrane treatment of cyanide water in the five cycle tests, the total content of cyanide in the permeating liquid was about 2 mg/L, which can meet the requirements of reverse washing of oxidized mineral cyanide residue. The concentration of thiocyanate and copper in the solution could be reduced to less than 5 mg/L and 15 mg/L, respectively, through the chemical reaction process. During the whole cycle, calcium ions increased from 300 mg/L to about 800 mg/L and then stabilized at about 800 mg/L. This may have occurred because in the backwashing process, acidic backwash water reacts with lime or calcium hydroxide in oxidized mineral cyanidation tailings to form calcium sulfate [29; 30]. In addition, part of the calcium sulfate precipitation is discharged with the filter cake, and at the same time, the concentration of calcium and sulfate ions in the solution is close to the saturated solubility of calcium sulfate. In addition, the backwashed cyanide tailings in the five cycle experiments met the requirements for storage in a tailing pond in TSPC. Compared with the existing AVR and SART processes, this process adopts the first acidification and then vulcanization for copper precipitation, which had the advantages of good copper precipitation effect, low consumption of sodium hydride sulfide and no secondary wastewater generation [20; 31; 32; 33]. And the treated acidic water in this process was used as backwash water to wash the alkaline cyanide tailings, so there was no need to add alkali for neutralization, and there is no acid wastewater discharge. What's more, the process adopts gaseous membrane to absorb HCN, which had high absorption efficiency and low energy consumption compared with the traditional inflatable volatilization reabsorption [17]. In summary, the \"filter press  
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**Steps** & **Process** &