One-step disposal of Cr (VI)-bearing wastewater by natural pyrrhotite

Cr(VI)-bearing wastewater can be treated by natural pyrrhotite which is use d for reductant to reduce Cr(VI) and precipitant to precipitate Cr(LU) simu ltaneously. The disposal products can be divided into three parts in the be akers, namely supernatant in the upper part, the yellowish colloidal precip itates in the middle part and the pyrrhotite in the lower part. The content of total Cr=Cr(VI)+Cr(LU) in the supernatant liquid is 0.06 mg/L, which is lower than 1.5 mg/L ct the discharge standard of China and near to 0.05 mg /L of the standard of potable water. This one-step disposal composing ct bo th reduction and precipitation which is traditionally divided into two inde pendent steps called reducing technology and precipitating technology respe ctively. The new method is of obvious economic advantage and favourable to decreasing surplus mud derived from adding Ca(OH)(2) to precipitate Cr(LU) traditionally so as to avoid recontamination. In fact, sodium sulfite (Na2S O3) used in disposal of Cr(VI) was traditionally produced from natural mine ral of pyrrhotite (FeS). One molecule of FeS is 4 times more than that of N a2SO3 from a view point of rational use of mineral resources. Therefore the prospective of application of the one-step disposal of Cr(VI) method is fu ll of promise.