Pyrite Flotation Research Articles

Effect of D-arginine as a novel depressant on the flotation separation of chalcopyrite from pyrite at low alkalinity

Flotation separation of Cu–Fe sulfide minerals typically necessitate the addition of substantial quantities of lime to depress pyrite flotation. Because lime can harm the environment, there is an urgent need to develop novel environmentally friendly depressants that are non-toxic and biodegradable. In this study, we investigated an environmentally friendly pyrite depressant containing amino and carboxyl groups, namely D-arginine (DA). The effect of DA on the surface hydrophobicity of Cu–Fe sulfide minerals and thus collector adsorption was investigated by analyzing zeta potentials, adsorption capacities, and contact angles. Additionally, changes in the surface properties of the minerals induced by DA were examined using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and atomic force microscopy (AFM). Flotation tests revealed that 2 × 10–4 mol/L DA reduced the flotation recovery of pyrite to 9.96 % at low alkalinity while leaving chalcopyrite recovery unchanged. The results of mineral surface analysis indicated that DA exhibited significantly stronger adsorption on the pyrite surface than on the chalcopyrite surface. Furthermore, DA effectively reduced the adsorption of the collector on the surface of pyrite, thereby weakening pyrite floatability at low alkalinity. Therefore, DA is a promising alternative depressant for the flotation separation of chalcopyrite from pyrite.

A comparison of dry and wet grinding on gold-bearing sulphide ore flotation

This study investigates the hypothesis that dry grinding prior to flotation can mitigate the adverse effects of galvanic interactions, improve the selectivity of gold flotation compared to wet grinding, and offer additional benefits due to water scarcity concerns and high water treatment costs. The effects of dry and wet grinding on the flotation behavior of gold-bearing sulphide ore were studied comparatively in terms of flotation test results and pulp chemistry parameters (pH, Eh, and dissolved oxygen). In addition, flotation tests without conditioning were also conducted following dry grinding in an attempt to minimize water contact further. Results demonstrated that dry grinding increased pulp potentials and dissolved oxygen levels, implying more oxidative conditions. Despite a lower mass pull with dry grinding, flotation recoveries and grades of gold and chalcopyrite were comparable to wet grinding, while dry grinding enhanced pyrite flotation at the rougher stage. Notably, flotation without conditioning effectively rejected pyrite and achieved higher grades for gold and chalcopyrite, indicating selective flotation. Therefore, dry grinding before flotation emerges as a viable alternative for gold and chalcopyrite flotation due to its improved selectivity while carefully optimizing flotation strategies and reagents to maximize recoveries.

Pyrite activation in seawater flotation by copper and lead ions: XPS and in-situ electrochemical investigation

Pyrite, as the main carrier of gold, can be collected via flotation which consumes high volumes of fresh water. Seawater is the promising alternative to fresh water, especially in the fresh water deficient regions. However, pyrite flotation is usually ineffective in seawater, which requires activation prior to recovery. This study mainly focuses on the roles of Cu2+ and Pb2+ on pyrite flotation in seawater. The flotation and contact angle results indicated that Cu2+ and Pb2+ obviously increased pyrite recovery in seawater by enhancing its surface hydrophobicity. Further XPS studies revealed that the formation of Fe-S-Cu(I) and Fe-O-Cu(II) on pyrite surface due to Cu2+ activation while the presence of Fe-O-Pb(II) and Fe-SO-Pb(II) due to Pb2+ activation, thereby improving the active sites and adsorption of xanthate. In addition, the in-situ scanning electrochemical microscopy (SECM) results showed that the formation of Cu2+ and Pb2+ activated products increased the electrochemical reactivity of pyrite surface, which was the main reason for the improved pyrite floatability. Moreover, the current consequence evolution indicated that pyrite activation by Cu2+ was stronger than that by Pb2+. The SECM imaging also showed that the adsorption of xanthate decreased the electrochemical reactivity on pyrite surface, with more significant role observing on the activated surface than that of the un-activated pyrite. It should be noted that the Cu2+/Pb2+ activation and xanthate adsorption were distributed unevenly on pyrite surface. This study therefore provides an in-situ approach to understand the role of inorganic ions and reagents on pyrite flotation in seawater, providing a promising strategy to use seawater for the flotation recovery of gold.

Acid mine drainage activation mechanism on lime-depressed pyrite flotation from copper sulfide ore

The lime-depressed pyrite from Cu differential flotation tailings with acid mine drainage (AMD) as a natural activator was recovered. The effect of AMD on lime-depressed pyrite flotation was investigated by a series of laboratory flotation tests and surface analytical techniques. Flotation test results indicated that AMD could effectively activate the pyrite flotation with a sodium butyl xanthate (SBX) collector, and a high-quality sulfur concentrate was obtained. Pulp ion concentration analysis results indicated that AMD facilitated desorption of Ca2+ and adsorption of Cu2+ on the depressed-pyrite surface. Adsorption measurements and contact angle analysis results confirmed that adding AMD improved the adsorption amount of SBX collector on the pyrite surface and increased the contact angle by 31°. Results of Raman spectroscopy and X-ray photoelectron spectroscopy analysis indicated that AMD treatment promoted the formation of hydrophobic species (S0 hydrophobic entity and copper sulfides) and the removal of hydrophilic calcium and iron species on the pyrite surface, which reinforced the adsorption of collector. The findings of the present research provide important theoretical basis and technical support for a cleaner production of copper sulfide ores.

Separation of galena and pyrite via green organic macromolecules at low alkalinity: Flotation response and surface adsorption mechanisms

Pyrite must be separated from galena during the beneficiation stage because it releases toxic gases during pyrometallurgy. However, the separation of the two minerals presents a huge obstacle as they have comparable hydrophobicity. This work offers an environmentally friendly pyrite depressant, pullulan polysaccharide (PP), for concentrating galena. Single mineral flotation showed that the ability of PP to deteriorate floatability was significantly stronger for pyrite than for galena within the pH range of 6.00 − 12.00. PP preadsorption assisted in separating galena from pyrite in a low-alkalinity pulp. The recovery of galena was 71.20 % higher than that of pyrite in the binary mineral flotation system. Characterization results confirmed that the Fe sites of pyrite were more susceptible to forming a stable coordination with the O atoms of PP’s C−O−H group compared to the Pb sites of galena. PP can impede the sodium butyl xanthate (BX) sorption on the pyrite surface, thus effectively depressing the pyrite. By contrast, the sorption of BX onto the galena surface was unaffected by PP, and the galena remained floatable. Thus, PP could be considered as an alternative to conventional inorganic depressants in the galena–pyrite flotation system. This work provides a scientific reference for the green and sustainable exploitation of non-ferrous metal resources.

Совершенствование реагентных режимов флотации руд сложного вещественного состава

Pyrite copper-zinc (sulfide) and polymetallic ores in Russia are complex and rebellious mineral raw materials. The main processing technology for such ores is flotation. Enhancement of the flotation technology for such mineral raw materials is currently performed in several directions. The practice of copper-zinc ore processing proves that obtaining highquality zinc and pyrite concentrates is impossible without the use of various modifiers in the sphalerite and pyrite flotation process. Such reagents are copper (II), zinc and iron (II) sulfates in the alkali-calcic medium. Therefore, research was carried out to study floatation properties of sphalerite and pyrite in the alkali-calcic medium with addition of one of the indicated sulfates to the mineral flotation process. The effect of each of the sulfates of copper (II), zinc and iron (II) on the flotation properties of sphalerite and pyrite was studied during flotation of the mineral with butyl xanthate and dithiophosphate at pH equal to 8, 10, and 12. The aim of this work was to study the effect of the sulfhydryl collectors in presence of copper sulfates, zinc and iron for flotation of sphalerite and pyrite with the grain-size class of 0.074 + 0.044 mm from one of the Russian deposits.

Effect of lead ions treatment on the flotation behavior of lime-depressed pyrite in a butyl xanthate system

Pyrite is often found alongside other sulfide minerals and is typically suppressed by lime during industrial flotation to selectively enrich with other valuable minerals. Given the continuous depletion of mineral resources, recycling these suppressed resources has become necessary. Consequently, the reactivation of lime-depressed pyrite is crucial for its recovery via flotation. This study investigated the lead (Pb) nitrate to activate lime-depressed pyrite. Various analytical techniques, including micro-flotation tests, zeta potential measurements, contact angle measurements, ultraviolet–visible spectrophotometry, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM-EDS) were employed to investigate the activation mechanism of Pb2+ on lime-depressed pyrite. The treatment with Pb2+ resulted in a significant enhancement in the recovery of lime-depressed pyrite flotation, achieving a maximum recovery of 98.33 %. Analysis through zeta potential, XPS, and SEM-EDS revealed that Pb species reacted with lime-depressed pyrite surfaces to form Pb-S and Fe-O-Pb species. This reaction enhanced the active sites and adsorption of collectors on lime-depressed surfaces, consequently increasing the hydrophobicity of the pyrite particles.

Galvanic interaction between galena and pyrite with dithiothreitol and its effects on flotation performance

With the advancement of green mine construction and the increasing difficulty of lead–sulphur resources, the traditional lime high-alkalinity lead–sulphur separation technology has exposed many shortcomings. In this study, based on the galvanic interaction of galena and pyrite, an environmental-friendly depressant dithiothreitol (DTT) was used to separate pyrite and galena under low alkalinity. In addition, the mechanism of DTT was revealed by electrochemical, ion dissolution, contact angle, zeta potential and DFT calculation. The results indicated that the galvanic interaction between galena and pyrite promoted the oxidation of galena and the dissolution of Pb2+ from the surface of galena, and Pb2+ would be adsorbed on the pyrite surface and increase the floatability of pyrite. DTT could selectively depress pyrite at low alkalinity. The interaction mechanism of DTT was that DTT could weaken the galvanic interaction of galena and pyrite and complex lead ions. In addition, DTT was adsorbed on the pyrite surface through the Fe-S bond, and the pre-adsorbed DTT hindered the adsorption of DDTC on the pyrite surface, thus the pyrite flotation was depressed.

The Interaction between Iron Cyanide and Lead Ions in Pyrite Flotation.

Despite being a major cyanide species in the process water, it is unclear how iron cyanide influences pyritic gold ore flotation as well as how lead ions influence pyritic gold ore flotation in the presence of iron cyanide. This study aims at revealing the interaction of Fe(CN)63- and lead ions in pyrite flotation to investigate the strong depressing effect of Fe(CN)63- on pyritic gold ore flotation and the significant activating effect of lead ions on pyritic gold ore flotation in the presence of Fe(CN)63- using flotation, zeta potential measurement and surface analysis methods. The flotation results showed that upon 5 × 10-5 mol/L Fe(CN)63- addition, pyrite recovery drastically decreased from about 51.3% to 8.6%, while the subsequent addition of 9.5 × 10-4 mol/L lead ions significantly activated pyrite with the recovery increasing from 8.6% to 91%, which demonstrated that Fe(CN)63- strongly depressed pyrite flotation, while lead ions completely activated pyrite in the presence of Fe(CN)63-. Zeta potential measurement, surface analysis using Cryogenic X-ray photoelectron spectroscopy (Cryo-XPS) and electrochemical impedance spectroscopy (EIS) revealed that Fe(CN)63- depression was attributed to the chemical adsorption of Fe(CN)63- on iron sites of pyrite as Prussian Blue (Fe[Fe(CN)6]); however, this hydrophilic layer could be covered totally by lead ions which adsorbed on as lead hydroxide/oxide through electrostatic interactions, which resulted in the significant activation effect of lead ions. The results from this study will lead to improved flotation of gold associated with pyrite in gold flotation plants.

Activation flotation of lime-depressed pyrite with carbon dioxide: Performances, mechanism and pilot-scale application

Activation flotation of lime-depressed pyrite by sulfuric acid (H2SO4) is usually accompanied by safety hazards and environmental pollution. Exploring eco-friendly, economical and effective activator to replace H2SO4 holds great significance for the sustainable development of mining industry. In this study, carbon dioxide (CO2) as a potential activator was applied in activation flotation of lime-depressed pyrite. Micro-flotation experiments results showed CO2 significantly improved the floatability of pyrite, and a maximum recovery of 93.94% was achieved under optimal operating conditions. The activation mechanism was investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Results indicated the depression of pyrite by lime was attributed to the formation of iron oxide/hydroxide species and calcium film, and CO2 effectively eliminated these hydrophilic compounds from the surface of pyrite, thus promoted the adsorption of xanthate onto the pyrite surface. Moreover, the anodic oxidation of xanthate on pyrite and the influence of CO2 on this process were investigated by cyclic voltammetry measurements. It was found that xanthate oxidation to form dixanthogen was more likely to occur in the presence of CO2, and this reaction replaced pyrite surface oxidation as the dominant anodic process. Finally, pilot-scale experiments were successfully conducted and the recovery of pyrite reached 93.18%, surpassing the ore dressing index of using H2SO4 as activator in actual production at the same period. Moreover, the concentration of sulfate ions in mineral processing wastewater was significantly reduced, and the annual cost of activator can be saved by 0.52 million RMB. The new process of activation flotation pyrite with CO2 has prospects for large-scale application in terms of activation performance, cost-effectiveness and environmental impact.

Flotation separation of chalcopyrite from pyrite and sphalerite using a novel collector: An experimental and mechanism investigation

In this paper, a new collector, named O-isobutyl-N-allyl thionocarbamate (IBATC), was synthesized, and the structure was characterized by Fourier Transform Infrared Spectrometer (FTIR) and 1H NMR, 13C NMR analysis. The collection performance of IBATC was evaluated by flotation tests and interaction mechanism was investigated by means of adsorption amount, zeta potential measurements, FTIR, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculation. The flotation tests results proved that IBATC was inclined to collect chalcopyrite compared with pyrite and sphalerite. Especially in the pH range of 9.5–10 and IBATC concentrate of 30–40 mg/L, the recovery of chalcopyrite exhibited more than 80 %. The adsorption amount and zeta potential measurements showed that IBATC had a greater orientation to chalcopyrite. FTIR and XPS analysis demonstrated IBATC chemically adsorbed on chalcopyrite surface, whereas physically adsorbed on pyrite and sphalerite. Further, DFT calculation of the interaction between IBATC and chalcopyrite proved that S atom of IBATC donated electrons to Cu sites on chalcopyrite surface and the adsorption energy was −19.45 kcal/mol, referring to an exothermic reaction. As a result, IBATC showed great capacity for the separation flotation of chalcopyrite, pyrite and sphalerite.

Research on resource comprehensive utilization of granite-type sulfide mine tailings

In order to recover and utilize mica and quartz from the tailings of a granite-type sulfide ore in Jiangxi Province, the technique of separating mica and quartz from the tailings by flotation without acid was investigated. Pyrite flotation was performed on a 500 g tailing sample to remove pyrite. And the middlings were acquired by desliming of the unfloated products. Finally mica and quartz was separated from the middlings in the mechanical flotation cell. Under conditions of pH=10.3 with a pulp concentration of 35% and a collector concentration of 180 g/t, a yield of 12.89% mica and 42.73% quartz was obtained, with silica grades as high as 71.50% in the quartz. The mica and quartz products can be used in construction ceramics and construction sand, respectively. It is believed that the outcomes of this work could provide ideas for comprehensive utilization of sulfide tailings.

Solving the mystery of natural pyrite flotation – A mineralogy-based approach

Many different types of pyrite have been observed in the mineral processing industry, varying in texture, chemical composition, electrochemical properties, and flotation response. One particular type of pyrite has been noted for its unusual behaviour is framboidal or “carbonaceous” pyrite. Specifically, a long history of carbonaceous pyrite presence has been recorded and studied at Glencore's Mount Isa Mines.This work is a detailed examination of the mineralogical characteristics of ore samples containing different pyrite types, to determine the underlying drivers of natural pyrite flotation. The work also revisits the original hypothesis that pyrite floatability is facilitated by the presence of carbonaceous material within the mineral matrix.Overall, this work closely mirrored that of previous studies, with the results closely aligned. The main difference is that when multiple ore domains are subjected to the same analysis, the flotation behaviour of carbonaceous content and pyrite appear to be independent. Instead, excessive natural flotation recoveries of pyrite are likely to be driven by factors that include the effect of galvanic interactions between chalcopyrite and pyrite.

The effect of cathodic surface areas on galvanic interactions between grinding media, chalcocite and pyrite and subsequent mineral flotation

Sulphide mineral processing often involves grinding media and a number of types of sulphide minerals at various ratios of feed grades, but conventional studies on galvanic interactions for sulphide mineral processing often looked into dual-phase galvanic contacts with an equal surface area of anode and cathode. For the first time, this study investigated the galvanic interaction of a tri-phase galvanic system (GM-Cc-Py) consisting of grinding media, chalcocite and pyrite with different surface area ratios of pyrite to chalcocite (Py/Cc) to reflect the practical nature. The electrochemical studies found that chalcocite acted as a cathode in the galvanic system in the absence of pyrite, but it was switched to an anode after the addition of pyrite at Py/Cc = 1. An increase in pyrite surface area not only further anodised grinding media and chalcocite, but also increased the galvanic interaction and the oxidation of anodic materials. This nature of galvanic interactions was found to impact the pulp chemistry after grinding and also the mineral flotation behaviour. A greater pyrite surface area caused a more reducing pulp condition and higher chalcocite oxidation, both promoting copper activation on pyrite and then pyrite flotation. This study identified a high amount of pyrite recovered in copper mineral flotation at a high pyrite feed grade and suggested solving this problem by altering the cathodic role of pyrite.

Evaluate the Depression of High-Concentration Pyrite in Copper Flotation by High-Chromium Grinding Media

ABSTRACT The copper (Cu) concentrators have to process high-pyrite-content ores due to rapid depletion of high-grade ores and a high demand for Cu by clean energy technologies. However, depressing high-concentration pyrite in copper flotation is challenging presently. For the first time, this study evaluated 30 wt% Cr steel, a type of high-chromium (HiCr) steel grinding media, which can effectively produce a high Cu concentrate grade in processing low-concentration pyrite ores, in treating 25% pyrite in a Cu feed at 1.7% Cu in comparison with treating 5% pyrite in a Cu feed at the same Cu grade. Flotation tests showed decreased Cu grade and Cu recovery as pyrite feed grade increased from 5% to 25%, which was attributed to the changed galvanic interaction between grinding media and sulfide minerals, supported by ethylene diamine-tetra acetic acid disodium extraction, pulp chemistry measurements, and electrochemical studies. As pyrite feed grade increased from 5% to 25%, the anodic role of 30 wt% Cr steel did not change, but the anodic role of chalcopyrite and the cathodic role of pyrite were enhanced, promoting chalcopyrite oxidation while retarding pyrite oxidation, both of which facilitated copper activation on pyrite and subsequent pyrite flotation. This study also compared 30 wt% Cr steel and traditional forged steel in depressing 25% pyrite in the feed, and forged steel poorly depressed pyrite due to a strong anodic role of forged steel and a strong cathodic role of pyrite during the galvanic interaction leading to strong copper activation on pyrite. This study points to a direction how to depress high-concentration pyrite in copper flotation.

Thiol-Silylated Cellulose Nanocrystals as Selective Biodepressants in Froth Flotation.

The extraction of various minerals is commonly conducted through froth flotation, which is a versatile separation method in mineral processing. In froth flotation, depressants are employed to improve the flotation selectivity by modifying the wettability of the minerals and reducing their natural or induced floatability. However, the environmental impact of many current flotation chemicals poses a challenge to the sustainability and selectivity of the ore beneficiation processes. To mitigate this issue, cellulose, particularly nanocelluloses, has been explored as a potential alternative to promote sustainable mineral processing. This study focused on silylated cellulose nanocrystals (CNCs) as biodepressants for sulfide minerals in froth flotation. CNCs containing thiol silane groups or bifunctional CNCs containing both thiol and propyl silanes were synthesized using an aqueous silylation reaction, and their performance in the flotation of chalcopyrite and pyrite was investigated in the presence of a sodium isobutyl xanthate collector. The results showed that the modified CNCs exhibited preferential interaction between chalcopyrite, and the flotation recovery of chalcopyrite decreased from ∼76% to ∼24% in the presence of thiol-grafted CNCs at pH 6, while the pyrite recovery decreased only from ∼82% to ∼75%, indicating the efficient selectivity of thiol-silylated CNCs toward chalcopyrite depression.

Flotation separation influenced by the rheological properties of diaspore-pyrite mixed pulp

The effects of pyrite and diaspore with different particle sizes on the rheological properties of pulp with butyl xanthate added as a collector were studied, and the mechanism for rheological pyrite separation from diaspore by flotation was probed. The apparent viscosity of the diaspore pulp with different particle sizes was higher than that of pyrite, especially for -30 μm diaspore. Microfine diaspore was an important component affecting the apparent viscosity and yield stress of the diaspore-pyrite mixed pulp, and the pulp became a non-Newtonian fluid when the mass fraction of fine-grained diaspore in the mixed pulp was high. In this study, sodium hexametaphosphate (SHMP) was used to control the rheology of the mixed pulp and improve the pyrite flotation, and the S (sulfur) recovery rate first increased and then decreased with increasing SHMP concentration. The apparent viscosity of the pulp decreased by 3.01% and the S recovery rate increased by 34.83% when the amount of added SHMP was 0.05 mg/kg. The apparent viscosity with 0.50 mg/kg SHMP was 21.76% lower than that seen with the addition of 0.05 mg/kg SHMP, but the S recovery rate was also reduced by 14.94%. Further research showed that the increased SHMP concentration led to increases in the electronegativities of the particle surface and the repulsive force between particles, which prevented agglomeration of the particles, reduced the apparent viscosity and yield stress of the mixed pulp, promoted collisions between the pyrite particles and the bubbles, and reduced the resistance of the air bubbles to flotation.

Mixed Anionic/Cationic Collectors for Pyrite Flotation: An Experimental and Theoretical Study

ABSTRACT The presence of pyrite causes harmful environmental and metallurgical effects during the pyrometallurgical processes of metals. Hence, various processing methods should minimize the amount in the feed. Meanwhile, flotation is one of the most common methods due to the natural hydrophobic property of the pyrite surface. Based on this premise, this research focuses on the efficiency of pyrite flotation using mixed anionic/cationic collectors as one of the significant factors of flotation. This study is organized and performed in two laboratory and simulation sections. Lab-scale studies consider the kind of collector(s), collector(s) concentration, size, frother concentration, and pH as practical factors. Dodecyl amine (DDA), potassium amyl xanthate (PAX), and Sodium Isopropyl Xanthate (SIPX) are three types of collectors examined in the single and mixed forms for pyrite flotation. In the simulation part, adsorption of a single form and mixed forms of collectors on the pyrite (001) surface and its effects on the wetting property of the surface is investigated using the molecular dynamics approach. In sum, the results of this study show that, although pyrite has the favorable ability of flotation with anionic collectors from the xanthate family (PAX and SIPX) due to its natural hydrophobic feature, the presence of a cationic collector (DDA) significantly enhances its flotation performance so that a 1:1 mixture of DDA and PAX with a concentration of 15 for each collector, at pH 7, and the presence of an A65 as frother (30 ), increases the flotation recovery of pyrite by more than 95%.

3D Characterization of Auriferous Pyrite Flotation Samples for Liberation and Grain Exposure Analysis Using Micro X-Ray Computed Tomography

3D Characterization of Auriferous Pyrite Flotation Samples for Liberation and Grain Exposure Analysis Using Micro X-Ray Computed Tomography

Selective flotation of chalcopyrite from pyrite via seawater oxidation pretreatment

The flotation separation of chalcopyrite from pyrite has attracted increasing attention due to the consumption of vast water resources and depressants. This study proposed the seawater oxidation pretreatment for non-depressant flotation separation of chalcopyrite from pyrite, as an effective and environmentally friendly strategy. Without the addition of depressants, seawater oxidation for 3 d effectively depressed pyrite flotation, with the highest recovery difference greater than 70% and a selectivity index greater than 6 between chalcopyrite and pyrite. The surface investigation showed that pyrite surface was more readily oxidized to form hydrophilic Fe oxidants/oxyhydroxides, as compared to that of chalcopyrite. Further UV-visible spectrophotometer and Fourier transform infrared spectrum (FTIR) results indicated that xanthate was less adsorbed onto the treated pyrite surface, resulting in un-floatable particles. Chalcopyrite surface was changed slightly due to seawater oxidation, thereby insignificantly affecting its flotation. The coordination theory was further used to reveal the combination mechanisms between xanthate and pyrite or chalcopyrite. This study therefore provides a promising strategy to effectively separate chalcopyrite from pyrite, especially in the freshwater-deficient area.