Process for reducing selenium and mercury from aqueous solutions

A process for removing mercury and selenium impurities from an acidic scrubbing solution comprising the steps of:

• mixing the acidic scrubbing solution with sodium sulfide to precipitate mercury and selenium from the acidic scrubbing solution;
• mixing the acidic scrubbing solution with sodium dithionite to cause precipitation of selenium from the acidic scrubbing solution;
• and
• filtering solids from the acidic scrubbing solution.

A process for treating an acidic solution, resulting from scrubbing gases produced in a process for preparing sulfuric acid, to recover selenium, comprising the steps of:

• mixing the acidic solution with sodium sulfide;
• mixing the acidic solution with sodium dithionite to precipitate the selenium;
• and
• filtering the selenium from the acidic solution.

A process for recovering mercury and selenium from an acidic solution, resulting from scrubbing gases produced in roasting zinc calcine to prepare sulfuric acid, comprising the steps of:

• filtering calcine from the acidic solution;
• mixing the acidic solution with sodium sulfide;
• mixing the acidic solution with sodium dithionite;
• filtering mercury and selenium solids from the acidic solution;
• and
• sending the treated acidic solution to effluent treatment.

A process for removing selenium from an acidic scrubbing solution, used to scrub impurities from gas produced by roasting zinc calcine, comprising the steps of:

• treating the solution with sodium sulfide to precipitate a first portion of the selenium;
• treating the sodium sulfide treated solution with sodium dithionite to precipitate a second portion of selenium;
• and
• filtering the sodium dithionite treated solution to produce a cake containing the precipitated first and second portions of selenium.