Recovery Of Trace Elements Research Articles

Efficiency of acid digestion procedures for geochemical analysis of tungsten mining wastes

There is an increasing global demand for tungsten, which is a critical element used in various industries. There are millions of tons of current and legacy mineral processing tungsten tailings worldwide that can potentially contaminate the environment and pose human health risks. These tailings could also become valuable resources if we thoroughly characterize their geochemical composition. In this study, an innovative method was developed to achieve the complete digestion of tungsten tailings. We tested three different digestion methods (hotplate digestion, bomb digestion and ColdBlock TM digestion) and compared the results. Additionally, an alkali fusion for major element analysis was applied and tested. The results showed that alkali fusion is the best method for major element analysis, while bomb digestion is best for tungsten and trace element analysis, although volatile chlorite loss was also observed. The hot plate digestion method was not recommended, owing to poor recovery of trace elements compared to the bomb digestion method. The quicker and safer ColdBlock TM digestion method can be used for bismuth, molybdenum, and several rare-earth element analyses, as indicated by their recovery being close to that from the bomb digestion method.

Multielemental determination of trace mineral elements in seawater by dynamic reaction cell inductively coupled plasma- mass spectrometry after Al(OH)3 coprecipitation

A simple method has been developed for the simultaneous determination of 12 trace mineral elements in seawater using, in some cases, several target isotopes (51V, 52Cr, 55Mn, 58,60Ni, 59Co, 63,65Cu, 64,66,68Zn, 75As, 78Se, 111,113Cd, 206,207,208Pb y 238U) in seawater. The method combined a simple and fast Al(OH)3 co-precipitation method, to pre-concentrate mineral elements and to separate them from the seawater matrix, and inductively coupled plasma mass spectrometry using the dynamic reaction cell with NH3 gas to do quantitative determinations free from polyatomic interferences. The recoveries of trace elements after Al(OH)3 co-precipitation varies between 80% for 111Cd and 116% for 59Co, which evidenced the accuracy of the method developed. The determination of 52Cr must be carried out by ICP-MS in standard mode due to the excess errors obtained using the proposed methodology.

Solid-phase extraction microfluidic devices for matrix removal in trace element assay of actinide materials

Advances in sample nebulization and injection technology have significantly reduced the volume of solution required for trace impurity analysis in plutonium and uranium materials. Correspondingly, we have designed and tested a novel chip-based microfluidic platform, containing a 100-µL or 20-µL solid-phase microextraction column, packed by centrifugation, which supports nuclear material mass and solution volume reductions of 90% or more compared to standard methods. Quantitative recovery of 28 trace elements in uranium was demonstrated using a UTEVA chromatographic resin column, and trace element recovery from thorium (a surrogate for plutonium) was similarly demonstrated using anion exchange resin AG MP-1. Of nine materials tested, compatibility of polyvinyl chloride (PVC), polypropylene (PP), and polytetrafluoroethylene (PTFE) chips with the strong nitric acid media was highest. The microcolumns can be incorporated into a variety of devices and systems, and can be loaded with other solid-phase resins for trace element assay in high-purity metals.

Rapid determination of copper and lead in Panax notoginseng by magnetic solid-phase extraction and flame atomic absorption spectrometry

Fe3O4/graphene magnetic nanoparticles were synthesized and used as adsorbents for the dispersive solid-phase extraction of copper and lead in Panax notoginseng. The properties of the nanocomposites were characterized by Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The effects of parameters like the adsorbent amount, pH, adsorption time, mutual ion interferences, desorption solution and reusability of the adsorbent for the recovery of trace elements were examined. Copper and lead were then quantified using a flame atomic absorption spectrophotometer. Under the optimized conditions, the detection limits for copper and lead were 0.22 and 0.87 μg L−1, respectively. Repeatability (within 1 day) and reproducibility (between days) of the method were less than 2.2 and 4.8 %, respectively. The proposed method was applied for determination of Cu and Pb in Panax Notoginseng and satisfactory relative recoveries (96.4–102.0 %) were achieved.

Development of Melting System for Measurement of Trace Elements and Ions in Ice Core

We present a titanium (Ti) melting head divided into three zones as an improved melting system for decontaminating ice‐core samples. This system was subjected to performance tests using short ice‐core samples (4 × 4 cm2, ~5 cm long). The procedural blanks (PBs) and detection limits of ionic species, with the exception of , were comparable with published values, but for elements the experimental procedures should be refined to obtain valid Zn concentrations due to the PB of ~90.0 ± 16.2 ng/L. The improved melting system efficiently decontaminated the samples, as verified by the concentration profiles of elements and ions in the melted samples from the three melting‐head zones. The recovery of trace elements in ice‐core samples was ~70–120% at ~100 ng/L in artificial ice cores. Because of the memory effects between ice‐core samples melted in series, the melting system should be rinsed at least 5–6 times (in a total volume of ~2.5 mL deionized water) after each melting procedure. Finally, as an application of this technique, trace elements were measured in ice‐core samples recovered from the East Rongbuk Glacier, Mount Everest, (28°03′N, 86°96′E, 6518 m a.s.l.), and the concentrations of trace elements following mechanical chiseling and the melting method were compared.

Solid phase extraction of Cd, Pb, Ni, Cu, and Zn in environmental samples on multiwalled carbon nanotubes.

A simple and sensitive solid phase extraction (SPE) method on multiwalled carbon nanotubes (MWCNTs) is presented for the determination of cadmium, lead, nickel, copper, and zinc at trace levels combined with flame atomic absorption spectrometry. The effects of parameters like pH, sample volume, sample and eluent flow rates, eluent concentration, and volume and type of eluent on the recovery of trace elements was examined. The metals retained on the nanotube at pH 6.5 as α-benzoin oxime complexes were eluted by 10 mL 2 M HNO3 in acetone. The influence of matrix ions on the developed method was also evaluated. The preconcentration factor of the method was found to be 50. The detection limits for Cd(II), Pb(II), Ni(II), Cu(II), and Zn(II) were found as 1.7, 5.5, 6.0, 2.3, and 2.4 μg L(-1), respectively. To test the accuracy of the method, the method was applied to TMDA-70 fortified lake water and Spinach 1570A standard reference materials. Addition recovery studies were applied to tap water and cracked wheat samples, and determination of the analyte elements was carried out in some food samples with good results.

Extraction of trace elements in human fluids using cation exchange resin (chelex-100) columns for ICP-MS analysis

A successful metal ion extraction method was developed using cation exchange resin packed disposable micro pipette tip columns for the extraction of trace metal ions in human fluids. Using this method, concentrations of Mn, Ni, Cu, Zn, Cd and Pb ions in human urine were determined by inductively coupled plasma mass spectroscopy (ICP-MS). The main objective of this study was to develop a technique to overcome spectral interferences in ICP analysis of trace elements in biological fluids mainly due to salts present in the samples. The amount of resins packed to the column, amount of eluent needed to extract trace elements, and particle size of the resin were examined to determine conditions for metal extraction. The validity of this technique was evaluated by calculating recoveries of trace element concentrations of above elements in certified standard urine samples and by using the technique for trace metal spiked urine samples. The results revealed that Pb, Cd, Zn, Cu and Mn had good recoveries (about 95%) while Ni & Co had about 80% recovery. It was also found that the recoveries of trace elements depended on the concentrations of relevant elements in the samples.Journal of the University of Ruhuna 2013 1(2): 23-30

Determination of Zirconium, Niobium, Vanadium and Chromium in the Titanium Ore by Microwave Digestion – ICP-OES

Abstract: Appropriate ratio of mixing digestion solvent which consist of HF and HNO3 have been tested firstly and combine with the high-pressure sealed microwave heating method, the titanium ore samples can be quickly and completely digested into solution. Then the elements content of zirconium, niobium, vanadium, chromium can be determined at the same time by applying the inductively coupled plasma atomic emission spectrometry (ICP-OES) method under hydrofluoric acid media condition.This method has solved the problem that the titanium ore matrix and impurities of zirconium oxide, niobium oxide, chromium oxide and other insoluble oxides are all difficult to digeste under normal conditions by the acid. Through fluoride ion complex reaction, make sure the easy hydrolysis of titanium ore matrix and niobium, zirconium and other elements to form the shape of the complex ion, even in the low acidity of the solution does not produce the hydrolysis reaction, so that it can greatly reduce the detection solution acidity to eliminate the blank background and acidity effects. The experiments investigated the impacts between the sample digestion conditions such as microwave heating procedures, reagents ratio, amount, and the titanium matrix as well as coexistent elements. Besides, it optimized the detection parameters of the ICP spectrometer under the conditions of using unconventional resistance to hydrofluoric acid PTFE nebulizer. Spectral interferences and matrix effects have been eliminated by selecting the appropriate analyte spectral lines as well as the integrated use of matrix matching and synchronization of the background correction method. The results show that the background equivalent concentration is 0.0002% ～ 0.0008%, and the detection limit is 0.0029 ～ 0.0018%, trace element recovery rate is 91.0% and ～108.0%, RSD is ≤ 4.71%.

Experimental investigation of the effects of mineral dust on the reproducibility and accuracy of ice core trace element analyses

Determination of trace element concentrations by inductively coupled plasma mass spectrometry (ICP-MS) can yield valuable information about paleoclimate from ice core records. Typically, ICP-MS analyses are performed on melted and acidified ice core samples which contain particulate material i.e., mineral dust. This particulate material is usually enriched in trace elements relative to ice core samples. Consequently, it is important to constrain the effect of acidification on mineral dust present in ice core samples and to assess the contribution of dust leaching to the trace element budget of ice cores. We have conducted a systematic experimental investigation designed to replicate the conditions of conventional ice core trace element analyses. Powdered rock standards of various lithologies were leached in 1 wt.% HNO 3 and the leachates were sampled at regular time intervals. Oxides and sheet silicate minerals, in the ferromanganese nodule (Nod-P-1) and granite (JG-2) leachates respectively, released available trace elements into solution relatively quickly; trace element recovery reached 57% for Mg and 42% for Mn in the granite leachate and recoveries between 60 and 80% were reached for most elements in the ferromanganese nodule leachate after only 12 h of leaching. In contrast, mafic minerals in the basalt (BHVO-2) and dolerite (W-2) released trace elements slowly, achieving recoveries of < 20% for elements from Li to Mn after 12 h of leaching. The mafic minerals continued to release trace elements into solution over several weeks causing Al and Ti concentration increases to > 4000%. These results demonstrate that acidification of ice core samples containing mineral dust will cause time- and mineral-dependent leaching of trace elements. Leaching behaviour of trace elements remained constant with varying mineral dust concentration but freezing pre-acidified samples was found to promote leaching of some trace elements. Ideally, all ice core samples would be fully digested or filtered to eliminate the error introduced by partial dissolution of dust but this is time-consuming and impractical. We therefore recommend acidifying samples for as long as practical to reach a maximum leachable concentration. For datasets obtained by conventional methods, Al is identified as the most suitable element to use as a terrestrial tracer because it is leached to a uniform extent across all lithologies. Fundamental flaws are identified in the calculation of crustal enrichment factors which are likely to cause some elements to appear enriched as a result of incongruent leaching. Ratios of trace elements, in particular rare earth elements (REEs), leached from mineral dust will not reflect those of the dust and are not suitable as tracers of dust provenance.

A technique for sequential leaching of coal and fly ash resulting in good recovery of trace elements

Coal and fly ash contain many elements. These elements exist in different forms which may change throughout the coal combustion process. There are several processes, including X-ray techniques and leaching techniques by which studies have attempted to assess the form of a particular element in a sample. This work focuses on determining the leachability of selected elements sequentially leached in four extraction solutions: water, 1 M ammonium acetate, 3 M hydrochloric acid and 50% hydrofluoric acid. The emphasis is on evaluating the steps involved in the leaching process with the mass recovery for each element being the basis for evaluation. The total amount of each element that will leach out under the given extraction condition is presented as a fraction of the total present in the material. The materials evaluated were NIST coal and fly ash standards. The elements measured in this study include aluminum, barium, beryllium, calcium, chromium, cobalt, iron, magnesium, manganese, nickel, potassium, sodium, strontium, vanadium and zinc.

Health risk assessment of trace elements in Chinese raisins produced in Xinjiang province

The concentrations of arsenic and nine other metals in various of Thompson Seedless raisins from Turpan city (TPC), Tuokexun county (TKC), Shanshan county (SSC), Grape Valley (GV) and Hetian region (HTR), and other variety samples from GV were determined by the Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) and the Graphite Furnace Atomic Absorption Spectrometry (GF-AAS), and assessed for their quality by comparing element levels in samples purchased with permissible limits stipulated by various agencies and organizations. Certified plant reference material (GBW07605) was used in trace element recovery and method validations. The ranges obtained for the elements analyzed in mg/kg were as follows: arsenic (<0.007), cadmium (0.004–0.01), chromium (0.303–0.698), copper (3.70–7.37), iron (46.6–70.3), mercury (0.005–0.009), manganese (3.99–6.32), nickel (0.125–0.243), lead (0.007–0.014) and vanadium (0.035–0.052). Duncan’s multiple range tests were applied to observe significant variations ( P < 0.05 and P < 0.01) existing in the levels of some trace elements levels between different production areas and across both Thompson Seedless raisins and other variety raisins in China. Based on a 70 kg individual consuming 228 g of raisins per week or 32.6 g of raisins per day, the values of contribution of estimated daily dietary intake (EDDI) to the tolerable upper intake level (UL) or the adequate intake (AI), estimated weekly dietary intake (EWDI) to Guideline or permissible tolerable weekly intakes (PTWIs) posed no health risks to humans.

Improvements in Digestion Protocols for Trace Element and Isotope Determinations in Stream and Lake Sediment Reference Materials (JSd‐1, JSd‐2, JSd‐3, JLk‐1 and LKSD‐1)

Total dissolution is a critical step in geochemical analysis. Despite the number of published protocols, this issue still draws attention for sediment samples, which are particularly difficult to dissolve due to the common occurrence and high abundance of refractory phases such as zircon. We present tests of different chemical digestion procedures carried out on reference materials (RM) of stream (JSd‐1, JSd‐2 and JSd‐3) and lake (JLk‐1 and LKSD‐1) sediments from the Geological Survey of Japan (GSJ) and the Canadian Certified Reference Material Programme (CCRPM). We demonstrate that the fusion technique is not appropriate for our studies as not all elements of interest were recovered and blank levels were too high to permit further Sr and Pb isotopic composition measurements. Similarly, conventional HF+HNO3 dissolution methods were not efficient enough for detrital samples. Our preferred method involved using high pressure Teflon® vessel bombs in association with HClO4. This protocol ensured a complete dissolution of the powder, as well as a complete recovery of trace elements. Moreover, blank levels were sufficiently low that Sr or Pb isotope compositions could be measured from the same mother solution. We also tested the homogeneity of RM powders by performing tests on various amount of powder.

Counter-current chromatography for oil analysis: Retention features and kinetic effects

Application of counter-current chromatography (CCC) for oil analysis has been suggested for the first time. CCC looks very promising as a tool for pre-concentration and isolation of trace elements from oil. Features of stationary phase retention of two-phase liquid systems (oil or oil products–aqueous nitric acid solutions) in CCC have been investigated. The influence of physicochemical properties of crude oil and oil products used as a mobile phase on the volume of stationary phase (acidic aqueous solutions) retained in CCC was studied. Chromatographic behavior of several oil samples was studied. It has been shown that physicochemical properties of test oil influence its chromatographic behavior. Optimal values of density and viscosity ( ρ < 0.85 g/cm 3, n < 7 cSt) of crude oil and oil products that could be analyzed using CCC were estimated. The influence of the column rotational speed and flow rate of mobile phase on the stationary phase retention was also investigated. It is known that kinetic aspects (mass transfer of elements between phases) can play a very important role in selecting an optimal composition of stationary phase for the pre-concentration of elements from oil. The influence of nitric acid concentration in the stationary phase on mass transfer was studied. Kinetic characteristic for trace element recovery has been investigated for the optimization of pre-concentration conditions of trace elements from crude oil and oil products. The extraction recoveries of Zn, Mn, Fe, Ni, V, Cu, Cd, Pb and Ba by CCC in dynamic mode are in the range of 75–95% while they are lower than 35% under batch conditions.

Trace element content of fish feed and bluegill sunfish (Lepomis macrochirus) from aquaculture and wild source in Missouri

Trace element content of fish feed and bluegill sunfish muscles (Lepomis macrochirus) from aquaculture and natural pond in Missouri were determined using the inductively coupled-plasma optical emission spectrometer (ICP-OES) and the direct mercury analyzer (DMA). Dietary intake rates of trace elements were estimated. Dogfish muscle (DORM-2) and lobster hepatopancreas (TORT-2) reference standards were used in trace element recovery and method validations. The average elemental concentrations (mg/kg diet, dry wt.) of fish feed were: As 1.81, Cd 2.37, Co 0.10, Cr 1.42, Cu 8.0, Fe 404, Mn 35.9, Ni 0.51, Pb 9.16, Se 1.71, Sn 20.7, V 0.09, Zn 118 and Hg 0.07. The mean elemental concentrations (μg/kg wet wt.) in bluegill muscles from both aquaculture and wild (in parenthesis) sources were: As 0.36 (0.06), Cd 0.28 (0.01), Co 0.0 (0.0), Cr 0.52 (0.05), Cu 0.38 (0.18), Fe 17.5 (2.43), Mn 0.18 (0.24), Ni 0.18 (0.04), Pb 1.03 (0.04), Se 0.34 (0.30), Sn 0.66 (0.42), V 0.02 (0.01), Zn 6.97 (9.13) and Hg 0.06 (0.24). Kruskal–Wallis chi square indicated significant differences in As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Sn, V, Zn and Hg (P<0.001), Se (P<0.01) and Mn (P<0.05) across the sampling locations. Dietary intake rates, estimated from weekly consumption of 228g of aquaculture and wild bluegills, posed no health risks for approximately 85% of all samples.

Preconcentration of trace elements by using 1-(2-Pyridylazo)-2-naphthol functionalized Amberlite XAD-1180 resin and their determination by FAAS

In this study, Amberlite XAD-1180 resin functionalized by 1-(2-pyridylazo)-2-naphthol (PAN) was synthesized and the resulting resin was used for preconcentration of Cr(III), Mn(II), Fe(III), Ni(II), Cu(II), Cd(II) and Pb(II) elements present at trace levels in different matrices. For this purpose, the copolymer was nitrated, reduced to the corresponding amine, converted to the diazonium salt with nitrite and reacted with PAN to produce the XAD-1180-PAN chelating resin. For the described method, the effect of some analytical parameters, such as pH, sample volume, resin amount, flow rates of uptake and stripping, volume and type of eluent, on the recovery of the trace elements was investigated. The metals retained on the XAD-1180-PAN resin were eluted by 2 mol L-1 HNO3. The influence of matrix ions, i.e., Na(I), K(I), Ca(II) and Mg(II), on the recovery of trace elements was also examined by using the developed method when they occurred both individually and together. The repeatability of the method at the optimum conditions determined experimentally was investigated. The recovery values for all the elements, except for Cr(III), were found to be >92% and the relative standard deviation was <8.5%. The 3s/b detection limits for Cr(III), Mn(II), Fe(III), Ni(II), Cu(II), Cd(II) and Pb(II) were found to be 4.1, 0.13, 2.7, 1.2, 0.19, 0.06 and 0.13 µg L-1, respectively. The developed method was utilized for preconcentration and determination of Mn(II), Fe(III), Ni(II), Cu(II), Cd(II) and Pb(II) in tap water, rain water, and stream water, and of Ni(II), Cd(II) and Pb(II) in a certified reference material (RM 8704 Buffalo river sediment) by flame atomic absorption spectrometry (FAAS).

Comparison of three sequential extraction procedures to describe metal fractionation in anaerobic granular sludges

In the last few decades, several sequential extraction procedures have been developed to quantify the chemical status of metals in the solid phase. In this study, three extraction techniques (modified [A. Tessier, P.G.C. Campbell, M. Bisson, Anal. Chem. 51 (1979) 844]; [R.C. Stover, L.E. Sommers, D.J. Silvera, J. Water Pollut. Con. F. 48 (1976) 2165]; and the Bureau Communautaire de Reference (BCR) [K.F. Mossop, C.M. Davidson, Anal. Chim. Acta 478 (2003) 111]) were applied to study the distribution of trace (Co, Ni, Zn and Cu) and major (Mn and Fe) elements in two different anaerobic granular sludges from full-scale methanogenic wastewater treatment plants. The Stover scheme displayed a higher number of fractions that induces a poor recovery compared to the other schemes. The sequential extraction scheme recommended by BCR and the modified Tessier scheme gave similar trends and are sufficiently repeatable and reproducible for application in fractionation studies. However, the BCR scheme seems to be of limited utilisation to study anaerobic matrixes because the extraction stage for its reducible fraction may release substantial amounts of trace elements bound to the organic/sulfides fraction, and consequently, the recovery of trace elements in the oxide fraction may be overestimated at the expense of the oxidisable fraction. As a final conclusion, the modified Tessier scheme seems to be the most suitable scheme to study the metal partitioning in anaerobic granular sludges.

Measurement of Trace Elements in Marine Environmental Samples Using Solution ICPMS. Current and Future Applications

AbstractFor Abstract see ChemInform Abstract in Full Text.

Measurement of Trace Elements in Marine Environmental Samples using Solution ICPMS. Current and Future Applications

The strengths and weaknesses of using inductively coupled plasma mass spectrometer (ICPMS) measurements of samples in solution for marine environmental analyses using real world examples is discussed. ICPMS can detect nanogram per litre concentrations of trace elements but suffers from polyatomic interferences generated from the sample matrix. Most of the routine trace elements measured in marine biological tissue and sedimentdigests, with the notable exceptions of iron, chromium, vanadium, and selenium, are not subject to severe interferences. Low recoveries of trace elements from sediments are due to the inability of extraction acids to remove trace elements such as chromium and nickel from sediment matrices. The use of ICPMS offers the advantage that elements such as phosphorus, which previously required elaborate digestion procedures and a colorimetric determination, can be rapidly determined using nitric acid digestion alone. The use of flow injection coupled with ICPMS allows on-line preconcentration of trace metals and metalloids using chelation by ion-exchange resins or hydride generation and trapping as well as separation from matrix elements. Thus, the routine determination of trace elements and inorganic and methylated arsenic, antimony, mercury, and germanium species in open-ocean waters is possible. The coupling of HPLC and GC to ICPMS allows the measurement of metal and metalloid species in biological and sediment extracts. However, extraction of unaltered species from matrices presents a challenge. Many of the species found in the environmental samples are not known and analytical standards are not available. The concurrent use of HPLC-MS is needed to confirm these species.

Trace element analysis of high purity arsenic through vapour phase dissolution and ICP-QMS

Vapour phase dissolution (VPD) has been used for the dissolution of high purity arsenic through acid vapours generated by aquaregia mixture, prior to trace element characterization. Trace impurities in As were determined by employing ion-exchange and volatilization methodologies for quantitative separation of the As matrix. After dissolving the As matrix through VPD procedure, sample solution in 0.1 M HF medium was loaded on Dowex-50WX8. The sorbed elements were then eluted first with a 20 ml aliquot of 4 M HNO 3 followed by another 10 ml of 6 M HNO 3 for the elution of REE (La, Ce, Gd and Lu). In the volatilization procedure, arsenic was removed from H 2SO 4 medium as volatile bromide by three successive additions of HBr at a temperature of about 220 °C. The trace element determinations were carried out by ICP-QMS. In both the matrix separation procedures namely on Dowex-50WX8 in 0.1 M HF medium and volatilization from H 2SO 4+HBr medium showed that the removal of arsenic matrix was nearly quantitative (>99.99%). The recoveries of trace elements were found to be >95%. Good agreement was obtained for many elements in both the procedures. The VPD approach provides considerable reduction of the process blank levels for all the elements when compared with conventional open dissolution approach. The subsequent ion-exchange or volatilization steps, contribute more to the overall process blanks.

Integrated system for complete usage of components in seawater: A proposal of inorganic chemical combinat on seawater

Very severe troubles of scale formation might be expected when the recovery of water from seawater increases. The main constituents of the scale are CaCO 3, Mg(OH) 2 and CaSO 4, all of which are salts of alkaline earth metals. Therefore, if a key technology will be developed by which the main constituents of the scale, all alkaline earth metal can be removed and/or separated from sea water, the recovery of desalted water from raw sea water by high pressure reverse osmosis (HPRO) can be increased up to 75–80%, the solubility limit of the remaining scale components. Then, it will be possible to make use of all valuable materials existing in sea water by an integral system which combines conventional recovery technologies with a set of the proposed technologies such as HPRO, alkaline earth metal ions removal process, inorganic ion-exchangers for recovery of trace elements and so on.