Treatment and recycling technology of tungsten polymetallic sulfide ore separation wastewater

All kinds of flotation agents such as xanthate, black drug and pinol oil generally used in the flotation process of sulfide ore separation plant, even if they are converted into organic compounds such as phenols through complex chemical and physical reactions, the wastewater discharged after treatment is organic pollution wastewater. The direct reuse of mineral processing wastewater without treatment, the coexistence of useful and harmful components of residual flotation reagents in mineral processing wastewater may disturb the sensitive separation process, reduce the concentration index, destroy the flotation reagent system, and it is difficult to adjust timely and effectively, affect the production operation of mineral processing, resulting in the loss and waste of mineral resources. The treatment technology of mineral processing wastewater is an important premise to realize the resource utilization of mineral processing wastewater. If it can be effectively recycled after treatment, it will become an important water resource for mine production. It is beneficial and harmless from the perspective of saving water resources or from the perspective of sustainable development of enterprises.The effect of different kinds of flocculants and coagulants on COD removal was studied by coagulation sedimentation method, and the adsorption technology was used to explore the further purification effect of wastewater, and the beneficiation experiment was conducted on the treated wastewater.

1. Material properties and test methods
1.1 Water quality analysis and test impact
The contents of harmful metal ions, organic matter and suspended matter in wastewater were analyzed, and the analysis results were shown in Table 1

The results in Table 1 show that, compared with the on-site production water, the COD content in the heating demedicated wastewater is mainly excessive, the SS content is too high, and the metal ion content is less. It shows that the main factors affecting the direct return of backwater are residual chemicals and suspended substances. The residual reagent will affect the reagent system of the existing process, and the suspended substance will be covered on the surface of coarse minerals on the one hand, and on the other hand, because of its strong adsorption capacity, it is easy to be entrained, thus affecting the flotation effect and concentrate quality.

The results show that the wastewater directly returned to the flotation operation has a great impact on the recovery rate of the concentrate, and the grade of the concentrate product is slightly reduced, indicating that the wastewater after dedusting is not suitable for direct return to use. Therefore, an experimental study was carried out on the wastewater.
1.2 Test methods
Coagulation method is a common physical method to treat mineral processing wastewater, it is mainly by adding coagulant to the wastewater, through neutralizing destabilization, rolling, adsorption bridge, sediment net trapping, compression double electric layer and other functions, so that the stable colloid in the wastewater is destabilized and condensed into large particle floc and settlement. This process can remove most of the SS, most of the heavy metal ions and some of the COD in the wastewater. Coagulation and precipitation method is the mainstream treatment method of wastewater from the selection plant at present, which has the advantages of simple process and low cost. Therefore, the test results have a stronger guiding significance for the production of the selection plant. The method of coagulation and precipitation + adsorption is adopted to treat the wastewater, and the residual agent is adsorbed and removed in the water to achieve the purpose of quality improvement.

2. Test results and discussion
2.1 Traceability analysis of sulfide ore separation wastewater exceeding the standard
In order to find out the cause of excessive COD and suspended matter content in demedicated wastewater, the source analysis was carried out. The effects of adding three organic agents butyl xanthoxanthate, terpineol oil and diesel oil as well as suspended matter on the COD content of wastewater were mainly investigated in the flotation process. The test results are shown in Figure 2.

As shown in FIG. 2, the effect of terpineol oil on the COD content of wastewater is the most significant, followed by diesel oil, and butyl xanthate has a small effect. The COD content of each flotation reagent wastewater is above 150mg/L, indicating that the residual flotation reagent is the main reason for the excessive COD content in wastewater. In addition, the concentration of suspended solids also has an impact on COD. The COD content of wastewater increases with the increase of the concentration of suspended solids, especially when the concentration of suspended solids increases from 15mg/L to 35mg/L, the increase is very obvious, indicating that suspended solids will also have a certain impact on the COD of wastewater. Therefore, whether the COD content and suspended matter content in wastewater can be reduced is the key point of whether the return water can be reused.
2.2 Study on flocculation and sedimentation law of wastewater
The type and dosage of flocculant and coagulant aid, stirring time, pH, adding sequence will affect the effect of flocculation settlement, so the flocculation settlement is studied systematically.
2.2.1 Comparative study of different flocculant combinations
XN-3 is a modified product of polyacrylamide (PAM) and belongs to anionic flocculant. Its structural units contain amide groups, easy to form hydrogen bonds, so that it has good water solubility and high chemical activity, easy to graft or crosslinking to obtain a variety of modifiers with branched chain or network structure, has a wide range of applications. The experiment investigated the effect of combined flocculant PAM+ PAC and new flocculant XN-3+PAC on reducing COD content in sulfide ore separation wastewater, and the results of the combined flocculant sedimentation test were shown in Figure 3.

The results of FIG. 3 show that the new combined flocculant XN-3+PAC can reduce the COD content in wastewater to 112mg/L, which is lower than the combined effect of natural sedimentation and PAM+PAC. Therefore, XN-3+PAC was subsequently used for the test.
2.2.2 Influence of flocculant and different coagulant AIDS on COD of wastewater
The effects of the combination of XN-3 flocculant with PAC, aluminum sulfate, polyferric chloride (PAF), ferric chloride and other coagulant AIDS on the COD content of wastewater after flocculation settlement were respectively investigated in the experiment. The addition sequence was 20mg/L coagulant first followed by XN-3 flocculant, and the test results were shown in Figure 4. As shown in Figure 4, the settling effect of XN-3 with polyaluminum chloride and polyferric chloride is better than that of aluminum sulfate and ferric chloride, and the appropriate dosage of XN-3 is 25mg/L. After comparison, polyaluminum chloride is selected for follow-up study.

2.2.3 Influence of coagulant aid on COD of wastewater
PAC is a common coagulant aid, it is a kind of polyhydroxyl, polynuclear complex cationic inorganic polymer compound. It has the advantages of obvious water purification effect, fast flocculation and precipitation speed, wide pH range, low corrosion to pipeline equipment, and can effectively remove suspended matter, COD and arsenic, lead, mercury and other heavy metal ions in water. The study found that the combination of PAC and XN-3 had an ideal effect, so the dosage of PAC was tested and the test results were shown in Figure 5.

As shown in FIG. 5, COD content in wastewater decreased significantly with the increase of PAC dosage, and basically stabilized when the dosage was 20mg/L. Therefore, the appropriate dosage of PAC was determined to be 20mg/L.
2.2.4 Influence of reagent addition sequence on flocculation settlement
The effects of the addition sequence of coagulant aid PAC and flocculant XN-3 on the flocculation settling effect were investigated. The test results are shown in Figure 6.

FIG. 6 shows that when flocculant PAM is added first, COD content in wastewater is significantly higher, and coagulant aid PAC is added first, which can effectively guarantee the interaction between PAC and wastewater and is conducive to flocculation and settlement.
2.2.5 Influence of COD in pH wastewater
The pH of wastewater is also one of the important factors affecting the flocculation settlement. Therefore, the influence of adjusting the pH of wastewater on the COD content of the water after flocculation settlement is shown in FIG. 7.

The results of FIG. 7 show that when the pH of wastewater is in a neutral to weakly alkaline environment (pH=7~8.5), the COD content in wastewater after flocculation and sedimentation is the lowest. Therefore, the pH of wastewater should be controlled to be neutral for flocculation and sedimentation.
2.3 Experimental study on adsorption law of flocculation wastewater
2.3.1 Comparative test of adsorbent types
The COD content in the wastewater after flocculation and sedimentation can be further reduced after passing through the adsorbent with porous structure. The demedicated wastewater after treatment is called "modified return water". The adsorbents commonly used in wastewater treatment are activated carbon, fly ash, slag, diatomite and so on. Activated carbon is a common adsorption material with huge specific surface area and abundant pore structure. Fly ash is an important secondary resource with wide source and low price. It can also be used as adsorbent after modification. Slag is a porous alkaline substance, which can also be used in wastewater treatment. Based on this, a comparative study was conducted on the types of adsorbents in wastewater after flocculation and settlement. In the test, 100mL wastewater after flocculation and settlement was selected and adsorbents 2g were added respectively for adsorption test. The test results are shown in Figure 8.

As shown in FIG. 8, the COD content in wastewater after adsorption can be further reduced, especially when activated carbon or modified fly ash is used, the COD content can be reduced to 93mg/L. Considering that fly ash is difficult to recycle in industrial application, industrialized mature activated carbon is selected as the adsorbent for follow-up test research.
2.3.2 Adsorbent dosage test
100mL of wastewater after flocculation settlement was selected and the amount of activated carbon as adsorbent was tested. The test results are shown in Figure 9.

FIG. 9 shows that the amount of activated carbon increases; The COD content in wastewater decreased significantly, and when the amount reached 20g/L, the COD content basically tended to be stable. Therefore, the appropriate amount of activated carbon was determined to be 20g/L.
2.3.3 Adsorption stirring time test
The adsorption stirring time has a great influence on the adsorption effect. Therefore, the experiment selected 100mL wastewater after flocculation settlement and 2g activated carbon to carry out the adsorption stirring time test. The test results are shown in Figure 10.

FIG. 10 shows that when the adsorption stirring time reaches 40min, the COD content basically tends to be stable; when the stirring time exceeds 40min, the COD content increases instead, which is because the resolution rate is higher than the adsorption rate because the adsorption stirring time is too long, so the adsorption stirring time is selected as 40min.
2.3.4 Adsorption stability test
The activated carbon adsorption stability test was carried out on the flocculation wastewater. The test conditions were as follows: the amount of activated carbon was 20g/L and the adsorption time was 40min. The test results were shown in Table 3.

The results in Table 3 show that after activated carbon adsorption treatment, the COD content of flocculating wastewater is reduced to 93.5mg/L, and the removal rate is 29.22%. So far, after flocculation sedimentation and adsorption treatment, the COD removal rate reached 49.46%.
2.4 Influence of reuse of modified wastewater on the selection index
Beneficiation test was carried out on the reformed backwater, and the test results are shown in Table 4.

It can be seen from Table 4 that except for the reduction of molybdenum grade of molybdenum concentrate, the modified return water has little effect on the separation grade and recovery rate of copper, molybdenum and bismuth, indicating that the heating dedrug wastewater can be reused in different stages after the modified treatment and achieve zero discharge.

3. Conclusion

1) Compared with the production water, the COD content of the wastewater after heating and depharmacizing is higher, as high as 334mg/L, the SS content is higher, as high as 33.53mg/L, and the content of other metal ions is not significantly different from that of the production water. The recovery rates of molybdenum, copper and bismuth concentrate decreased by 11.66, 11.03 and 19.62 percentage points respectively, indicating that the return water was not suitable for direct reuse.

2) The trace analysis results of the exceedance items in the wastewater after heating and depharmacizing show that butyl xanthate, terpineol oil and diesel oil have an impact on the exceedance items, among which terpineol oil has the most significant impact on the COD content of wastewater, followed by diesel oil, and butyl xanthate has the least impact. In addition, high suspended matter is also one of the reasons for the high COD content.

3) When XN-3+PAC is used as flocculant + coagulant aid, the COD reduction effect is the most obvious. The appropriate dosage is (25+20)mg/L, the appropriate settling time is 120min, the addition sequence is PAC, XN-3, and the appropriate settling pH range is neutral to weakly alkaline (pH=7~8.5). The COD in wastewater decreased from 185mg/L to 133mg/L, and the COD removal rate was 28.10%.

4) When activated carbon is used as the adsorbent, the COD reduction effect is the most obvious. The appropriate dosage is 20g/L and the adsorption stirring time is 40min. After adsorption, the COD content decreases from 132.1mg/L to 93.5mg/L, and the COD removal rate is 29.22%.

5) Compared with the small-scale test, the return water after flocculation, sedimentation and adsorption has little effect on the separation grade and recovery rate of copper, molybdenum and bismuth except that the molybdenum grade of molybdenum concentrate is reduced, which indicates that the heating dedrug wastewater can be reused in different stages after modification treatment and achieve zero discharge.