Removal of chemical oxygen demand and ammonia nitrogen from high salinity tungsten smelting wastewater by one-step electrochemical oxidation: From bench-scale test, pilot-scale test, to industrial test.

In recent years, electrochemical oxidation (EO) shows the characteristics of green and high efficiency in removing chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) from wastewater, which has been favored by researchers. However, at present, most of current studies on EO remain in laboratory stage, reports about pilot-scale or even industrial tests with large treatment capacity are few, which slowing down the use of the advanced technology to practical application. In this study, bench-scale tests, pilot-scale tests (treatment capacity 200-500 L/h), and industrial tests (treatment capacity 100 m3/h) were carried out by EO technology in view of the characteristics of tungsten smelting wastewater (TSW) with high salinity (NaCl), COD, and NH3-N. Results showed that the removal of COD and NH3-N was a competitive reaction in the EO process, and COD could be removed more preferentially than NH3-N. When NH3-N content was low, the influent pH had a minimal effect on its removal, and when NH3-N content was high, increasing the influent pH was beneficial to its removal. Industrial tests showed that the one-step removal of COD and NH3-N in TSW met the standard, and the power consumption per cubic meter of wastewater was only 4.2 kW h, and the treatment cost was much lower than the two-step process of "breaking point chlorination to remove NH3-N and adding oxidant to remove COD". This study has successfully realized industrial application of EO technology in TSW treatment for the first time and provided a successful case, which is helpful to accelerate the popularization and application of this technology in the field of high salinity organic ammonia nitrogen wastewater treatment.

Efficient removal of NaOl from mineral processing wastewater using Al-electrocoagulation.

Sodium oleate (NaOl) is widely used as collector for oxidised ore flotation, and residual NaOl in mineral processing wastewater is a serious threat to mine environment. In this work, the feasibility of electrocoagulation (EC) as an alternative for chemical oxygen demand (COD) removal from NaOl-containing wastewater was demonstrated. Major variables were evaluated to optimise EC, and related mechanisms were proposed to interpret the observations in EC experiments. The initial pH of the wastewater greatly affected the COD removal efficiency, which was likely to be related to the variation of predominant species. When the pH was below 8.93 (original pH), liquid HOl(l) was the predominant specie, which could be rapidly removed by EC thought charge neutralisation and adsorption. At original pH or higher, Ol- could react with dissolved Al3+ to form insoluble Al(Ol)3, which was subsequently removed through charge neutralisation and adsorption. The presence of fine mineral particles could reduce repulsion force of the suspended solids and promote flocculation, whereas the presence of water glass had an opposite effect. These results demonstrated that EC can be employed as an effective process to purify NaOl-containing wastewater. This study will contribute to deepening our understanding of EC technology for NaOl removal and provide useful information to researchers in mineral processing industry.