Study of innovative materials for the removal of high concentrations of fluoride from water for drinking and domestic use

Natural fluoride contamination of drinking water is a serious issue that affects several countries of the world. The consumption of water with fluoride concentration higher than 1.5 mg/L (WHO recommended limit) is recognized to cause serious diseases, and fluoride removal from natural contaminated waters is a health priority for more than 200 million people worldwide. The octacalcium phosphate (OCP), a mineralogical precursor of bio-apatite, is here tested as a fluoride remover. Fluoride removal experiments are performed in batch-mode using different initial concentrations of fluoride (from 40 to 140 mg/L) and reaction times. Most of fluoride is removed within the first two hours of all experiments, and the drinkable limit of 1.5 mg/L is reached within a minimum of 3 hours for an initial fluoride concentration of 40 mg/L. The experimental fluoride removal capacity of OCP is 25.7 mg/g, and 4 g of OCP can effectively treat 1 L of water with fluoride concentration up to 50 times higher than the drinking limit of 1.5 mg/L. XRD and chemical characterization of the solid phases, before and after the removal experiments, indicate that OCP transforms into fluorapatite (FAP) uptaking fluoride from solution. The property of OCP to be the crystalline precursor of apatite has been also investigated using equal molar amounts of fluoride, chloride, hydroxyl and carbonate anions dissolved in aqueous solution, in order to asses if and how the anionic competition can influence the formation of the different apatite end-members. The investigation, conducted through XRD, SEM and ICP-OES analyses, shows that fluoride is the main anion removed from solution during the OCP transformation, and consequently fluorapatite is the main resulting apatitic phase, followed by hydroxyapatite. With the aim to perform the field trial, a new device based on the application of OCP has been developed. The prototype (FLOWERED Defluoridator Device [FDD]) essentially is composed of a 20‐L tank and a recirculating pump that guarantees the interaction between water and OCP. The device is powered by a car battery for a fixed pumping working time using a fixed amount of OCP for every defluoridation cycle. The results of tests performed in the rural areas of Tanzania show that a standardized use of the prototype can lower the dissolved fluoride from an initial concentration of 21 mg/L to below the World Health Organization (WHO) drinkable limit of 1.5 mg/L in 2 h without secondary negative effects on water quality. The approximate cost of this device is around US$220, whereas that of OCP is about$0.03/L of treated water. As with any device, acceptance requires a behavioural change on behalf of rural communities that needed to be investigated. To this end, we piloted a survey to explore how psychological and socioeconomic factors influence the consumption of fluoride‐free water. Results show that the adoption of FDD and OCP is more appealing to members of the rural communities who are willing to pay more and have a high consumption of water. Moreover, we suggest that given the low level of knowledge about fluorosis diseases, the government should introduce educational programs to make rural communities aware of the negative health consequences

Willingness to pay for fluoride-free water in Tanzania: disentangling the importance of behavioural factors

Approximately 200 million people, mainly concentrated in rural areas of the Great East African Rift Valley, suffer from fluorosis caused by excess of fluoride naturally contained in water. This study employs the RANAS (Risk, Attitude, Norm, Ability, Self-regulation) model to understand how behavioural factors influence Tanzanian rural communities’ willingness to pay for fluoride-free water obtained from a new defluoridator device. Results show that perceived risk, knowledge, attitudes and descriptive norms significantly influence the adoption of the proposed healthy behaviour. Policy implications are discussed taking into account how rural communities could achieve equitable and affordable access to safe water

MINERALOGICAL STUDIES OF THE W-Sn VEIN SKARNS OF MONTE TAMARA (NUXIS, SULCIS DISTRICT): INSIGHTS FOR STRATEGIC MINERALS EXPLORATION IN SW SARDINIA (ITALY).

Skarn deposits are a relevant source of critical raw materials such as W, Sn, and In. Recent studies conducted in South Sardinia pointed out the relationships between various Sn-W-Mo deposits and the early Permian (289-286 Ma) F-bearing, ilmenite-series ferroan granites (e.g., Sulcis pluton). This new evidence triggered a broad re-examination of granite-related deposits including skarn deposits hosted by Cambrian limestones of the low-grade Variscan basement of the Sulcis district (SW Sardinia). With this purpose, field investigations and OM, SEM-EDS, EMPA, and LA-ICP-MS observations, and analyses have been conducted on the skarn ores of Monte Tamara (Nuxis, northern Sulcis) where scheelite has been reported in the old San Pietro and Sinibidraxiu mines. The San Pietro mine exploited a 1-5 m thick and 70 m deep, steeply dipping skarn orebody located at the tectonized contact between early Cambrian sandstones and limestones. The orebody includes layers of Grt-Cpx-Wo, magnetite, and Zn-Pb-Cu-Fe sulfide bands. Prograde and retrograde stages with oxides and sulfides can be recognized. Clinopyroxene is the foremost mineral of the prograde stage; garnets (andradite-grossular) are usually dark green with typical anomalous birefringence and distinctly zoned (Fe-rich cores and Al-rich rims). Hematite turned to mushketovite, and Mo-rich scheelite, followed by In-bearing cassiterite, occasionally occur in the prograde assemblages. Amphiboles and epidotes mark the retrograde stage, together with abundant Zn-Cu-Fe-Pb sulfides and accessory molybdenite, stannite, bismuthinite, and Bi-Ag-Pb sulfosalts. At San Pietro, dominant sphalerite displays highly variable Fe, Mn, and Cd contents. Relictlooking blebs of Fe-Mn-poor Sp are scattered in high-Fe-Mn Sp where Sn EMPA peaks may correlate with cassiterite-stannite micro-inclusions. Galena composition suggests localized intergrowths with micro-inclusions of bismuthinite, Bi-Se, and Bi-Te sulfosalts. The stannite-sphalerite geothermometer provided a temperature range of 325-200°C for the sulfide stage. The Sinibidraxiu old mine exploited a 1,5 m thick and 60 m deep columnar body, hosted in early Cambrian marbles. It consists of a sphalerite-wollastonite assemblage with late sulfides, quartz, and calcite, hosting cm-sized arsenopyrite and scheelite. Scheelite is Mo-poor; Sn-, other Mo-phases and Bi-phases are absent. High-Fe Sp, rimmed by low-Fe Sp and blebby galena, is finely intergrown with wollastonite cockades. The results from this study suggest that a wide range of skarn-related mineralizing phenomena occurred in the Monte Tamara area. Both orebodies resulted from a structurally controlled migration of metasomatic fluids inside the hosting carbonate formation. Mineral zonation and composition of the San Pietro skarn point towards skarn development under varying fO2 conditions, oxidizing then rapidly turning to moderately reducing within the prograde W-Sn skarn stage and into the sulfide stage. The features of the Sinibidraxiu orebody (e.g., Mo-poor, As-devoid scheelite) suggest a formation from reducing metasomatic fluids but S-poor compared to San Pietro, probably at more distal environments (e.g. low Sn-Bi contents). From this point of view, the Monte Tamara area still maintains an economic potential, linked to the possible presence of proximal skarn ores at depth; thereby representing a key area for further exploration for granite-related strategic and critical metals in SW Sardinia

Mineralogy of the scheelite-bearing ores of Monte Tamara, SW Sardinia: insights for the evolution of a Late Variscan W–Sn skarn system

Southwestern Sardinia, Italy, hosts several skarn, W–Sn–Mo greisen and hydrothermal deposits related to a 289±1 Ma Late Variscan granite suite. Among them, the most representative scheelite-bearing skarns belong to the San Pietro and Sinibidraxiu localities, in the Monte Tamara area, Sulcis region. The San Pietro deposit is a typical calc-silicate skarn whereas Sinibidraxiu is a sharply bounded orebody hosted in a marble unit. Optical petrographic observations and compositional data of major and trace elements were obtained for samples from both localities. San Pietro data suggests evolution from an oxidising prograde skarn stage (andradite–diopside, hematite and scheelite), to progressively more reducing conditions from the early retrograde (magnetite–cassiterite) to the late sulfide stage (arsenopyrite, stannite, molybdenite, Bi sulfosalts and Zn–Cu–Pb–Fe sulfides); Sinibidraxiu has diffuse carbonate–quartz intergrowths pseudomorphic over an early mineral assemblage with fibrous habit, followed by abundant ore mineral precipitation under reducing conditions (scheelite, arsenopyrite and Pb–Zn–Cu–Fe sulfides). Geothermometers indicate a comprehensive temperature range of 460–270°C for the sulfide stages of both deposits. The differences between the two deposits might be controlled by the distance from the source intrusion coupled with the different reactivity of the host rocks. The San Pietro mineralogy represents a more proximal skarn, contrasting with more distal mineralogical and chemical features characterising the Sinibidraxiu orebody (lack of Mo–Sn–Bi phases; LREE–MREE–HREE signature of scheelite). This investigation contributes for the first time to the identification of a W–Sn skarn system in SW Sardinia, thereby suggesting the Monte Tamara area and its surroundings as favourable for further exploration

First evidence of vivianite in human bones from a third millennium BC Domus de Janas : Filigosa tomb 1, Macomer (NU), Sardinia

Altres ajuts: Acord transformatiu CRUE-CSICSardinia is an island located in the middle of the Mediterranean Sea. Due to its position geologically acquired in the Middle Miocene (around 16 Ma ago), this island had a very strategic position in antiquity, as it was involved into all the trade routes that crossed the Mediterranean Sea; however, it developed original archaeological features up to the Iron Age. During the Final Neolithic, the Ozieri's Culture developed throughout the Sardinian territory, with diffusion of typically hypogea graves named Domus de Janas. The study was conducted inside the Domus de Janas at Filigosa necropolis, located on a tuffaceous hillside near the village of Macomer in the area of Marghine, Central-Western Sardinia. Tomb 1 dating back to the beginning of the third millennium BC had been excavated by Professor E. Contu in 1965 At the time of first excavation, this tomb showed very particular conditions that had enabled an excellent conservation of several osteological and wooden samples. This paper focuses on the presence of vivianite deposits on human bones and its origin. For such a mineral to be formed an interaction between phosphate, iron and water has to occur. These findings can be considered the first evidence of such mineral in a Sardinian archaeological site, and one of the most ancient findings of this mineral in Italy, as well as the first evidence observed in prehistoric sites related to a period before the introduction of iron use

METODO DI SINTESI DELLA MOLECOLA OTTACALCIO FOSFATO

L’invenzione è relativa ad un processo per la produzione di Ottacalcio fosfato a partire da carbonato di calcio e acido ortofosforico in cui il carbonato di calcio e l’acido ortofosforico sono posti a reagire in acqua secondo un rapporto molare compreso nell’intervallo 1,25-1,41, la massa di carbonato di calcio essendo compresa nell’intervallo 0,1-20 g per litro d’acqua, la temperatura di reazione essendo compresa nell’intervallo 55-85°C e la reazione essendo condotta per un intervallo di tempo fra 3 e 16 ore. Al termine della reazione, si recupera l’Ottacalcio fosfato dalla sospensione acquosa per filtrazione o decantazion

From a fluorite vein system to a five-element-type polymetallic vein system? The first evidence of Ni-Co minerals from the world-class, CRMs-bearing Silius deposit (SE Sardinia, Italy)

In recent years mineral sources of Critical Raw Materials (CRMs), whose supply is strategic and irreplaceable in many technological and industrial applications, have become the subject of growing interest throughout Europe. An excellent example is the Silius vein system (SE Sardinia), in which the mining activities, after several years of standby, are going to be resumed to exploit fluorite, galena and LREE minerals. This world-class deposit (2.2 Mt of proven reserves) consists of two main parallel, steeply dipping, ENE-WSW to NE-SW directed veins which coalesce at depth, hosted in Middle Ordovician metavolcanites, Upper Ordovician metasediments and Silurian black shales belonging to the Variscan Nappe Zone of SE Sardinia. The vein filling displays dominantly banded textures with abundant fluorite, quartz, calcite, galena, barite, and accessory base-metal sulfides (sphalerite, chalcopyrite and pyrite-marcasite), LREE carbonate (synchisite-Ce) and xenotime-Y. Sulfide contents in the ore increase downward. Knowledge about the trace elements content of sulfides in the deposits is still scarce, thus new underground surveys and samplings have been performed in three different levels of the mine. In samples collected from the deepest level (level 100 m a.s.l., Muscadroxiu sector), tiny inclusions of Ni-Co minerals have been found for the first time ever by optical microscopy (reflected light) and SEM-EDS analyses. They consist of very complex intergrowths dispersed in chalcopyrite and the quartz gangue, containing various associations of Ni-Co-Fe arsenides and sulfarsenides such as nickeline, rammelsbergite, gersdorffite, cobaltite and arsenopyrite. Remarkably, this assemblage is very similar to that found in the shallower parts of the nearby “Sarrabus Silver Lode”, a similar, regional-scale vein system exploited in the past for silver. Thus, it may be speculated that it not only could be a general indication of possible Ni-Co enrichments below the 100 level of the mine, but also an exploration tool and a proxy of possible Ag enrichments of the ore at depth. Moreover, the Ni-Co assemblages and LREE minerals found in Silius are similar to those found in the polymetallic (Ni-Co-As-Ag-Bi) veins of Southern Arburèse district (SW Sardinia), the five-element branch of the Montevecchio vein system, in the past a major Pb-Zn source in Italy. In addition to partly similar mineral assemblages, the Silius and Arburèse vein systems share a common derivation from lowtemperature and high-saline fluids, supporting their attribution to the unconformity-related group of five-element and fluorite-barite deposits well-known throughout central and western Europe (Erzgebirge, Odenwald, Schwarzwald, French Central Massif, Catalonian Coastal Ranges, Pennidic Alps, etc.). These deposits have been collectively connected to metallogenic events associated with the Late Paleozoic-Mesozoic breakup of the supercontinent Pangea, so Silius, the Arburèse and other similar Sardinian deposits could be related to this regional-scale event. In conclusion, the Silius vein system is a key area to understand the regional events that occurred after the Variscan orogeny in Sardinia; the deposit may represent a relevant source of CRMs and metals in Italy, where besides fluorite, base-metal sulfides and LREE, some concentrations of Ni-Co and, possibly, Ag minerals might be present at depth

Application of octacalcium phosphate with an innovative household‐scale defluoridator prototype and behavioral determinants of its adoption in rural communities of the East African Rift Valley

Natural fluoride contamination of drinking water is a serious issue that affects several countries of the world. Its negative health impact is well documented in the East African Rift Valley, where water consumption with fluoride concentration greater than 1.5 mg/L can cause fluorosis to people. Within the framework of the EU Horizon2020 “FLOWERED” project we have first designed an effective defluoridation device based on innovative application of octacalcium phosphate (OCP), and then explored its acceptance within rural communities. The prototype (Flowered Defluoridator Device, FDD) essentially is composed by a 20 L tank and a recirculating pump that guarantees the interaction between water and OCP. The device is powered by a car battery for a fixed pumping working time using a fixed amount of OCP for every defluoridation cycle. The results of tests performed in the rural areas of Tanzania show that a standardized use of the prototype can lower the dissolved fluoride from an initial concentration of 21 mg/L to below the WHO drinkable limit of 1.5 mg/L in 2 hours without secondary negative effects on water quality. The approximate cost of this device is around 220 USD, while that of OCP is about 0.03 USD per liter of treated water. As any device, acceptance requires a behavioral change on behalf of rural communities that needed to be investigated. To this end, we piloted a survey to explore how psychological and socioeconomic factors influence the consumption of fluoride‐free water. Results show that the adoption of FDD and OCP is more appealing to members of the rural communities who are willing to pay more and have a high consumption of water. Moreover, we suggest that given the low level of knowledge about fluorosis diseases, the government should introduce educational programs to make rural communities aware of the negative health consequences

Insights to promote safe drinking water behavioural changes in zones affected by fluorosis in the East-African Rift Valley

The presence of fluoride in drinking water can have beneficial effects in reducing the incidence of dental caries when its concentration lies in the optimal range of 0.5-0.7 mg/l. However, fluoride intake below and above this range can have negative effects on tooth enamel and skeletal fluorosis in case of prolonged exposure to high concentrations. Unfortunately, in some areas of the world, such as rural communities of the East-African Rift Valley (EARV), water is dramatically contaminated by fluoride which may cause dental and skeletal fluorosis because its concentration is often well above the maximum threshold of 1.5 mg/L recommended by the World Health Organisation. To tackle this problem experts and policy makers have attempted to introduce defluoridation techniques that, as well as being cost-effective, allow end users to drastically reduce the level of fluoride below the above-mentioned threshold. However, the adoption of these techniques remains quite low because behavioural factors influencing people’s safer water consumption in these areas of the world is poorly understood. To fill such a gap in this study we explore how these factors can influence the adoption of a new defluoridator in Kenyan and Tanzanian rural communities of the EARV. To achieve this objective 75 people belonging to Maasai and Meru ethnic groups were interviewed running nine focus groups where these factors were investigated using the RANAS (Risk, Attitude, Norm, Ability, Self-Regulation) model. Results show that the drinking behaviour of people living in the EARV is dramatically affected by contextual factors and exacerbated by the high level of fluoride naturally contained in drinking and cooking water. Behavioural insights into how policy makers and marketers could reverse this unhealthy drinking behaviour introducing technological devices that can cut the quantity of fluoride contained naturally are discussed arguing in favour of the possibility of using different behaviour changing techniques