The dependence of the solubility of NaLa(SO 4 ) 2 . H 2 O, NaCe(SO 4 ) 2 . H 2 O, KLa(SO 4 ) 2 . H 2 O, and KCe(SO 4 ) 2 . H 2 O on the concentration of acids in sulfuric, phosphoric, and sulfuric3phosphoric acid solutions containing up to 36 wt % H 2 SO 4 and 33.12 g l !1 H 3 PO 4 was studied at 20oC.The most promising method of the recovery of lanthanides from phosphogypsum and phosphosemihydrate, which are formed in the manufacture of phosphoric acid by the processing of apatite concentrate with sulfuric acid, is the sulfuric acid leaching [1,2]. Because these products contain sodium and potassium hexafluorosilicates, sparingly soluble double sulfates of lanthanides with sodium and (or) potassium can be formed in the leaching solutions. In addition, the sulfuric acid leaching solutions contain residual phosphoric acid from phosphogypsum. NaLa(SO 4 ) 2 . H 2 O and KLa(SO 4 ) 2 . H 2 O are poorly soluble in water [3, 4]. Data on the solubility of double sulfates MLn(SO 4 ) 2 . H 2 O in sulfuric and sulfuric3phosphoric acid solutions are lacking. The concentration of lanthanum and cerium oxides in the sum of lanthanide oxides in the apatite concentrate exceeds 70 wt % [5]. Therefore, data on the solubility of lanthanum and cerium compounds are especially important for understanding processes that occur in sulfuric acid leaching of lanthanides. The goal of this study was to determine the solubility of double sulfates M`M"(SO 4 ) 2 . H 2 O (M`= Na, K; M" = La, Ce) in sulfuric and sul-furic3phosphoric acid solutions of low and medium concentrations.
EXPERIMENTALWe used analytically pure grade chemicals. The double sulfates were synthesized by the standard procedure [4, 6], i.e., by evaporation of an aqueous solution containing lanthanide and alkali metal sulfates, with alkali metal sulfates taken in a 20% excess above stoichiometry. The precipitates were filtered off, the residual mother liquor was pressed out by filter centrifugation, excess alkali metal sulfates were removed from the mother liquor by washing with 3% H 2 SO 4 , the residue of the washing solution was pressed out by filter centrifugation, and the precipitate was dried at 1253150oC. The chemical analysis of the products synthesized (Table 1) was consistent (taking into account 3% error of the atomic absorption method used), and the X-ray phase analysis revealed no impurity phases. According to the thermogravimetric (TG) analysis, the products synthesized are monohydrates.The sulfuric3phosphoric acid solutions were prepared by adding small amounts of 85 wt % H 3 PO 4 into sulfuric acid solution of prescribed concentration c H 2 SO 4 ; the corresponding change in c H 2 SO 4 was neglected. The H 3 PO 4 concentration c H 3 PO 4 in the solutions was in the range typical of process solutions obtained from leaching of phosphosemihydrate waste with sulfuric acid.The content of lanthanides in the solutions was determined by oxalate gravimetric method [7] and by atomic-emission spectrometry with an inductively coupled plasma source on a Plasma 400 spectrophoto...
Temporally and spatially (55°-70°N) extensive records of mercury (Hg) in freshwater fish showed consistent declines in boreal and subarctic Fennoscandia. The database contains fish entries (n: pike>perch>>brown trout>roach≈Arctic charr) from 3132 lakes across Sweden, Finland, Norway, and Russian Murmansk area. 74% of the lakes did not meet the 0.5 ppm limit to protect human health. However, after 2000 only 25% of the lakes exceeded this level, indicating improved environmental status. In lakes where local pollution sources were identified, pike and perch Hg concentrations were significantly higher between 1965 and 1990 compared to values after 1995, likely an effect of implemented reduction measures. In lakes where Hg originated from long-range transboundary air pollution (LRTAP), consistent Hg declines (3-7‰ per year) were found for perch and pike in both boreal and subarctic Fennoscandia, suggesting common environmental controls. Hg in perch and pike in LRTAP lakes showed minimal declines with latitude, suggesting that drivers affected by temperature, such as growth dilution, counteracted Hg loading and foodweb exposure. We recommend that future fish Hg monitoring sampling design should include repeated sampling and collection of supporting information (pollution history, water chemistry, fish age, stable isotopes) to enable evaluation of emission reduction policies.
Harmful algal blooms (HABs) in arctic lakes are recent phenomena. In our study, we performed a long-term analysis (1990–2017) of the eutrophication of Lake Imandra, a large subarctic lake, and explored the biodiversity of bloom-forming microorganisms of a 2017 summer HAB. We performed a 16Sr rRNA metabarcoding study of microbial communities, analysed the associations between N, P, C, and chlorophyll concentrations in the lake water, and developed models for the prediction of HABs based on total P concentration. We have demonstrated that blooms in Lake Imandra occur outside of optimal Redfield ratios and have a nonlinear association with P concentrations. We found that recent summer HABs in a lake occur as simultaneous blooms of a diatom Aulacoseira sp. and cyanobacteria Dolichospermum sp. We have studied the temporal dynamics of microbial communities during the bloom and performed an analysis of the publicly available Dolichospermum genomes to outline potential genetic mechanisms beneath simultaneous blooming. We found genetic traits requisite for diatom-diazotroph associations, which may lay beneath the simultaneous blooming of Aulacoseira sp. and Dolichospermum sp. in Lake Imandra. Both groups of organisms have the ability to store nutrients and form a dormant stage. All of these factors will ensure the further development of the HABs in Lake Imandra and the dispersal of these bloom-forming species to neighboring lakes.
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