Technology of removing lead and recycling rare earth from saponified wastewater generated during process of rare earth extraction

Abstract

The invention discloses a technology of removing lead and recycling rare earth from saponified wastewater generated during the process of rare earth extraction. The technology comprises the following steps: (a) making saponified wastewater which is generated during the process of rare earth extraction go through an oil separation tank to remove the oil; (b) adding a NaOH solution, adjusting the pH to 10.5-13, and separating the solid and the liquid to obtain a supernate containing lead and rare earth precipitate; (c) subjecting the precipitate to plate-frame pressure filtration to obtain press filtrate and pressure-filtered residues; or dissolving the rare earth precipitate by hydrochloric acid or an acidic extractant to obtain a chlorinated rare earth solution, and the extracting rare earth from the chlorinated rare earth solution; (d) adding a Na3PO4 solution into the supernate and / or the press filtrate to obtain lead phosphate precipitate and supernate, wherein the content of total Pb in the supernate is not more than 0.2 mg / L; (e) press-filtering the precipitate, stacking the precipitate together, handing over the precipitate to factories, which has the qualification to process the dangerous solid wastes; acidifying the supernate, adding lime milk to remove the excess PO4<3->, then discharging the wastewater, wherein the content of total Pb in saponified wastewater is not more than 0.2 mg / L, the discharged wastewater can meet the requirements of Pollutant Discharge Standards Of Rare Earth Industry, and at the same time, the rare earth in the wastewater is effectively recycled.

Description

technical field [0001] The invention relates to a technique for step-by-step deep removal of lead and simultaneous recovery of rare earth from rare earth extraction saponification wastewater. Background technique [0002] Rare earth ores contain trace amounts of lead, arsenic, aluminum, uranium, thorium and other elements. In the process of extraction, smelting and separation of rare earths in an acidic system, extractants (organic phase) such as P507, P204 and naphthenic acid are used to pass through alkaline substances (sodium, Calcium, magnesium, ammonia and other basic compounds) after quantitative saponification, then mixed with an acidic rare earth solution with a pH of 1~4 for rare earth saponification (extractant loaded with rare earth ions), quantitative extraction of rare earth elements, resulting in trace rare earth ions and difficult to be Rare earth extraction saponification wastewater (pH=3.5~5) of the extracted heavy metal ions, after the wastewater is collect...

AI Technical Summary

Problems solved by technology

However, due to the difference in the pH of the initial formation and complete precipitation of different metal elements, some heavy metal elements cannot be completely precipitated and removed under the condition of meeting the water pollutant discharge limit pH=6~9, especially the discharge standard of rare earth industrial pollutants. (GB2645-2011 Table 2) The total Pb ≤ 0.2 mg / L requirement, there is a hidden danger of substandard discharge

At the same time, after solid-liquid separation and pressure filtration of the precipitate (inorganic sludge) generated by heavy metals such as rare earths and lead, the obtained hydroxides containing rare earths and heavy metals are all soluble in acid, and the rare earths in the wastewater cannot be directly recycled, which is a waste of rare earths. resources, reducing the recovery rate of rare earths in the production process

Even with PO4 3- or S 2- Rare earth and lead elements can be treated and removed, but rare earth phosphates and sulfides are insoluble in acid, and cannot be directly separated from the rare earth extraction and saponification wastewater by precipitation and dissolution to separate heavy metals and recycle rare earths.

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