The behavior of thallium during jarosite precipitation

Abstract

Jarosite precipitation provides an effective means of eliminating thallium from zinc processing circuits, and a systematic study of the extent and mechanism of thallium removal during the precipitation of ammonium, sodium, and potassium jarosites was carried out. Thallium (as Tl + ) substitutes for the ''alkali'' ion in the jarosite structure. Nearly ideal jarosite solid solutions are formed with potassium, but thallium is preferentially precipitated relative to either ammonium or sodium. Approximately 80 pct of the dissolved thallium precipitates during the formation of ammonium jarosite; the extent of thallium removal is virtually independent of thallium concentrations in the 0 to 3000 mg/L Tl range and of the presence of 75 g/L of dissolved Zn. Although the deportment of thallium is nearly independent of (NH 4 ) 2 SO 4 or Na 2 SO 4 concentrations Ͼ0.1 M, the precipitates made from more dilute media are relatively enriched in thallium. Likewise, the precipitates made from dilute ferric ion media are also Tl-rich. Low solution pH values or low temperatures both significantly reduce the amount of jarosite formed, but the precipitates made under these conditions are enriched in thallium. Furthermore, because thallium jarosite is more stable than the ammonium or sodium analogues, the initially formed precipitates are consistently Tl rich. The presence of jarosite seed accelerates the precipitation reaction, but dilutes the thallium content of the product. The results suggest that most of the thallium in a hydrometallurgical zinc circuit could be selectively precipitated in a small amount of jarosite, by carrying out the precipitation reaction for a short time in the absence of seed and from solutions having low alkali concentrations.

Factors Affecting the Precipitation of Potassium Jarosite in Sulfate and Chloride Media

“…The near independence of the composition with increasing retention time is characteristic of the precipitation of most jarosite-type compounds. [17,19] …”

“…[19] Given the widespread natural occurrence of potassium jarosite and its potential importance in metallurgical processing, a systematic series of experiments was carried out to define the parameters affecting the precipitation of potassium jarosite (KFe 3 (SO 4 ) 2 (OH) 6 ) over a wide range of solution concentrations and at temperatures up to 220°C. The results of these studies are presented in this report.…”

Complex sulphide-barite ore leaching in ferric chloride solution

“…The determination of the optimal leaching rate is thus the major object in this study, because the values of leaching rate published in various papers and especially those obtained by investigations with natural concentrates exhibit great scatter. Dutrizac [16] observed significant differences ~ 50% in leaching rates of eleven chalcopyrites from different localities under various leaching conditions. The scattering results can be mainly attributed to admixtures and impurities as well as to the influence of real structure of the investigated material.…”

“…Ferric and cupric ions, bacteria, oxygen, and other oxidants have been used as leaching agents of sulphide in sulphate and chloride media under atmospheric or pressure leaching conditions [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

“…The oxidation potential of ferric chloride leaching system results in elemental sulphur as one of the major by-products, a form generally more acceptable environmentally than the sulphur dioxide from pyrometallurgy. The leaching of metal sulphide minerals in chloride media is a subject of interest and many articles have been published [12][13][14][15][16][17][18]. This studied indicated that the ferric chloride solutions could rapidly, but unselectively leach valuable metals such as copper, zinc and lead from sulphide minerals, leaving the bulk of the pyrite and sulphur.…”