Phosphate Mining Industry Research Articles

Anticorrosive pigment for smart and green protective coatings: An alkyd resin coating incorporating lanthanum-loaded hydroxyapatite, derived from a phosphate mining industry by-product

Intelligent anti-corrosive coatings have gained considerable interest as a method to protect metals. This approach offers an effective strategy for mitigating corrosion by providing advanced control over the process. In this research, lanthanum-loaded hydroxyapatite pigment (La-HAp) was successfully synthesized using phosphate sludge (PS) waste. The pigment was incorporated into an alkyd resin coating to provide smart corrosion protection for mild steel exposed to a saline solution. The synthesized pigments were characterized using various analytical techniques, including FTIR, XRD, and SEM−EDS. The inhibitory performance of La-HAp on mild steel submerged in a 3% NaCl solution was evaluated using linear polarization and EIS techniques. The findings demonstrated substantial inhibitory effectiveness, achieving 82% inhibition efficiency. Further investigation compared the protective capabilities of modified (C-La-HAp) and reference (C-Ref) alkyd coatings on carbon steel using EIS. The results indicated significant corrosion protection enhancement with 5% La-HAp, showing a polarization resistance of 19.7 MΩ·cm2 after four weeks of immersion in the aggressive solution. This corrosion resistance is primarily attributed to the formation of a barrier against the corrosive environment and the trapping of Cl- ions by the HAp, accompanied by the release of La, phosphate, and calcium ions. La ions react with OH- ions produced in the cathodic zones to form a uniform protective layer of Lahydroxides, while iron orthophosphates provide additional protection at anodic sites. This synergistic blend of mechanisms imparts intelligent corrosion-inhibiting properties to the alkyd resin, effectively guarding against the damaging effects of corrosive agents.

Assessment and Mitigation of Groundwater Contamination from Phosphate Mining in Tunisia: Geochemical and Radiological Analysis

Groundwater contamination in the Mediterranean Basin is a severe problem that has a significant impact on environmental ecosystems and human health. The unconventional uranium and the potentially toxic elements (PTEs) of phosphate rocks are the principal contaminants in the phosphate mining industry in Tunisia. Phosphogypsum (PG) results from the valorization of phosphate to fertilizers and phosphoric acid. PG stocks can be used in cement production, brick manufacturing, and soil amendments in desertic land, and can be resolved by using nanomaterial adsorbents. In the flat area of the study area, the increase in radioactivity (40K) is due to abusive fertilizer use. Geochemical and radiological analyses in the northern part of Tunisia and its karst shallow aquifer indicate significant contamination levels. The northern part exhibits moderate contamination, whereas the karst shallow aquifer shows higher contamination levels, particularly with elevated nitrate concentrations. In the phosphate basin, both washing phosphate and phosphogypsum reveal high levels of radioactive elements, with the latter showing especially high concentrations of radium. The shallow aquifer in this region has moderate contamination levels, while the deep geothermal aquifer also shows noticeable contamination but to a lesser degree compared to the shallow aquifer. The shallow groundwater is characterized by a higher value of radioactivity than the groundwater due to the contamination impact from the phosphate industry and the cumulative radioactivity disintegration. Finally, the nanoparticles and the electrostatic adsorption can decrease the PTEs and radionuclides from the contaminated water in the study area. Moreover, other key issues for advancing research on groundwater contamination are proposed in this study. It is time to valorize this PG and the other mines of (Fe, Pb, and Zn) in the socioeconomic sector in Tunisia and to minimize the environmental impact of the industrial sector’s extraction on groundwater and human health in the study area.

Phosphate mine by-products as new cementitious binders for eco-mortars production: Experiments and machine learning approach

Phosphate mining industry generates different types of by-products that have significant environmental impacts such as ecosystems destruction and soil contamination. To reduce their environmental footprint, these wastes were investigated as supplementary cementitious materials (SCMs). The generated by-products included a clayey material and calcareous marl which were used in the current study. Blends of the abovementioned materials with cement (ratio of 1:1) were investigated using X-Ray Fluorescence spectrometry (XRF), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TDA-TG), Mercury Porosimetry, Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Electromechanical testing device. Using these results, a learning model based on multiple linear regression (MLR) was proposed to predict the compressive strength and the specific surface area from the constituents of the material, the additives, the L/S ratio, and the hardening regime. The accuracy of the models was assessed using the correlation coefficient (R2), mean absolute error (MAE), and root mean square error (RMSE). Compressive strength results confirmed that the sample's strength improved with the amount of calcined clay. Unlike the water demand where the mixtures required more water than the OPC mixture. SEM-EDS examinations proved the existence of the C–S–H gel, responsible for the specimen strength. The used machine learning model demonstrated excellent performance and practical potential to predict both compressive strength (CS) and specific surface area (SS) by capturing both linear and nonlinear relationships. As well as time and plasticizer were the most influential factors on the properties studied (CS and SS) and their effect was positive. This sensitivity study provides important information on the critical factors influencing compressive strength and specific surface area in the different ranges considered.

Impact of Micro-NPR bolt on the mining of deep-buried phosphate via the room-and-pillar method

Large and complex goaf groups have formed as a consequence of mining activities in the Yichang Phosphate Mine. These goaf formations have given rise to recurring engineering challenges and disasters, including roof collapse and pillar damage, primarily attributed to excessive ground pressure. Owing to the working principle and mechanical properties of traditional PR bolts, the preload cannot be applied to the surrounding rock immediately after excavation, resulting in considerable roadway damage. To address the problem of large deformation control in deep mines, a damage mechanics model of a roof-and-pillars mine was established to analyse its deformation and damage characteristics. A physical model experiment was performed to analyse the damage state of the roof and pillars in a deep-buried phosphate mine with twin roadways using the room-and-pillar method. The objective was to examine the effectiveness of the PR and micro-NPR(negative Poisson's ratio) bolt support systems under real conditions. Experimental results indicated that the micro-NPR bolt effectively strengthened the roof and pillar, enhanced the strength and stiffness of the pillar, and prevented pillar extrusion and roof collapse. These findings bridge the gaps in the existing theoretical frameworks, technical research, and engineering applications of the micro-NPR support, promoting technological innovation in the phosphate mining industry. This study provides a reference for the state change and support research on the surrounding rock after the excavation of twin parallel tunnels under specific conditions.

Correlation of the Diffusion Parameters and the Biological Activities in the Formulation of Pinus halepensis Essential Oil in Phosphogypsum Material

The use of natural biopesticides, specifically essential oils, is being explored as an alternative solution to protect stored foodstuffs. This study focuses on a formulation of phosphogypsum–Pinus halepensis essential oil as a pesticidal product. First, the essential oil chemical composition was determined using gas chromatography with mass spectrometry (GC-MS), while the phosphogypsum (waste from the phosphate mining industry) was analyzed using scanning electron microscopy, X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric–differential thermal analysis; thus, physico-chemical properties and heavy metal contents were determined. In a second step, the preparation of the formulation consists in grafting the essential oil on the phosphogypsum (adsorption) in a cylindrical geometric shape adapted to the models applied in the bioprocesses of storage. The study of essential oil transfers in the material in the case of desorption along the axis (Oz) was carried out using analytical and numerical models of the Fickian diffusion process to understand the behavior of the oil and determine physicochemical parameters such as diffusivity (D) and evaporation flux (F). By using statistical methods such as experimental design and principal component analysis, these parameters can help explain the mechanisms involved in the insecticidal activities against the primary pest of lentils (Bruchus signaticornis) and in the parameters of lentil seed germination.

Phosphate waste rocks recycling in ceramic wall tiles: Technical performances

The phosphate mining industry produces large amounts of waste rocks during the open-pit mining operation. In the present paper, phosphate waste rocks, abundant in different regions of Morocco, are investigated as a candidate material for partial/entire replacement of conventionally used industrial minerals. Several recipes for the production of tiles are tested, based on raw materials from five representative phosphate waste rocks mine sites and a raw clay from Safi's region in Morocco. The phosphate waste rocks are shown to be mainly composed of phyllosilicates (smectite, sepiolite, and palygorskite), carbonates (dolomite and calcite), and silica frameworks (quartz, tridymite, and cristobalite) as major phases. The raw samples and calcined mixtures were characterized by using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transformed infrared spectroscopy (FTIR). Properties analyses revealed that the produced ceramic tiles can be classified as porous bodies. The tiles based on 100% of phosphate waste rocks have shown excellent mechanical properties (∼55 MPa) in terms of compression and they can be used in the traditional wall tiles called “Zellige” in Morocco.

Effect of flotation phosphorus tailings on the microstructure and compressive strength of white Portland cement

The phosphate mining industry produces large amounts of tailings. Rational utilisation of phosphorus tailings (PT) is of great significance for the full exploitation of waste resources and environmental protection. In this study, PT were used as one of the raw materials to prepare white Portland cement clinker (WPCC). Various techniques were used to study the effect of PT on the mineral composition, ionic solid solution and compressive strength of the WPCC. The results showed that using PT in WPCC significantly improved the burnability of the raw material, increased the liquid phase content and promoted the formation of minerals. The addition of PT was found to stabilise α′-C2S crystals and promoted the change of C3S crystals in the clinker from T-type to M-type. The addition of PT had no significant effect on the decomposition temperature of calcium carbonate, the appearance temperature of the liquid phase and the formation temperature of C3S. A PT content of 2.5% produced the highest strength of the WPCC: compared with the control group, the 3-day strength increased by 46.86% and the 28-day strength increased by 82.59%.

ASSESSMENT OF EXTERNAL OCCUPATIONAL DOSE OF PHOSPHATE MINE WORKERS IN SAUDI ARABIA USING THERMOLUMINESCENT DOSEMETERS.

Workers in the mining industry face the problem of radiation exposure from naturally occurring radioactive materials. Thus, this study aimed to estimate a Hp (10) doses for mine workers in the phosphate mining industry in Saudi Arabia. The personal dose equivalent [Hp (10)] of 606 mine workers in the phosphate mining industry in Saudi Arabia were obtained from 2016 to 2019 using thermoluminescent dosemeters (TLDs). The results showed that the annual mean Hp (10) of all mine workers averaged over the study period was 0.66mSv (SD=0.45), which is within the range of occupational doses reported worldwide. Most of the Hp (10) were <0.49mSv, and the maximum Hp (10) was 3.55mSv. Nonetheless, internal exposure should be evaluated along with external exposure to estimate a comprehensive baseline occupational dose for mine workers in the phosphate mining industry in Saudi Arabia.

Bridging the gap: Social divides and coalition building in the phosphate-mining industry in Jordan

ABSTRACT Research on coalitions mainly focuses on the formation of coalitions between well established, formally and politically organised groups. Less attention has been placed on coalitions that form between groups that are not formally organised but, nonetheless, identify themselves and others as clearly distinct social groups. Through the analysis of the coalition of employees that formed in the Jordan Phosphate Mines Company in 2011, this article argues that the study of such coalitions not only opens up new analytical perspectives for a better understanding of coalition building and its ‘transformative’ effects, but also represents an insightful analytical tool to investigate the micro-sociological dynamics of local political arenas. After examining the processes of dissociation and association that make the JPMC employees’ protest movement a coalition, the article discusses the effect of coalition building in reshuffling pre-existing divides, and the political significance of such reshuffling in the Jordanian context.

Groundwater vulnerability Mapping of Jordanian phosphate mining area based on Phosphate concentration and GIS: Al-Abiad mine as a case study

The present study uses DRASTIC model on a national rate and assess the groundwater contamination through phosphate release from the mining activities in south of Jordan (Al-Abiad area) using GIS environment. It is found that about 58.6% of the area was considered to be of moderate vulnerability, while high and low vulnerability was found to be at 0.6% and 42.8% respectively of the total area. On the other hand, investigation of infiltration process of selected pollutants (soluble phosphate and chloride ions) through the surface layer of study area has confirmed the vulnerability of the groundwater quality toward such as pollutants. Chemical analysis of the effluent washing water from the phosphate beneficiation process showed high concentration of P2O5 (TCP), Cl− and SiO2 comparing with influent washing water. Currently, the effluent water from Al-Abiad and other Jordanian phosphate mining industry is discharged into the desert without treatment or any attempt for reuse.

Desorption of La3+ and Ce3+ from Treated ‘Chert’ a Siliceous Byproduct of the Phosphate Mining Industry of Gafsa-Metlaoui Basin (Southwestern Tunisia)

Chert, the most abundantby-product of the phosphate mining industry, collected from the Metlaoui Gafsa basin underwent purification treatments and was characterized by various analytical methods (XRD, XRF, SEM, FTIR, laser granulometry). The obtained treated chert is a siliceous phase SiO2 (~ 98%) mainly composed of opal-CT (trydimite phase and cristobalite) and traces of quartz. The chert morphology is granular. Treated chert has been successfully tested and proved to be an effective sorbent of rare earths. In this study, the desorption of La3+ and Ce3+ from ion-loaded chert was investigated and the reversibility of sorption reaction was verified. Several eluting agents at different concentrations were tested to desorb those lanthanides such as mineral acids (HCl and HNO3), chloride salt (CaCl2) and ultra pure water. Results show that, HCl and CaCl2 are efficient eluents and the adsorbed Ce3+and La3+ can be easily eluted by them. However, the highest desorption percentages were achieved using calcium chloride as eluting agent (Ce3+, 93.651%; La3+, 96.446%). Kinetics of desorption of La3+ and Ce3+ from treated chert were studied. The rate of desorption was initially fast in the first 30 min, but gradually declined with time. Among all tested kinetic models, the pseudo-second-order model fits the kinetic data best with a better correlation coefficient (R2 > 0.9) and the desorption isotherms fitted better to freundlich, which means that lanthanum and cerium release was dominated by multilayer desorption process from heterogeneous and independent surfaces.

(Invited) Electrokinetic Separations to Increase the Percent Solids of the Effluent from a Phosphate Mine

Phosphate mining operations create a waste product, consisting of a dilute clay/sand/phosphate suspension that, due to the properties of the suspended solids (primarily clay), requires 25 to 50 years to densify via hindered settling and self-weight consolidation. The objective of this research was to develop and apply an effective electrokinetic separation process to phosphatic clay suspensions, generated during the beneficiation of phosphate ore, a major component of fertilizer. The use of an electric field to separate the water from the solids is attractive because the inherent stability of the clay suspension is due, in part, to the surface charges residing on the platelets.Previous work by others has demonstrated the feasibility of batch-wise electrokinetic separation of phosphatic clay suspensions, but the process is widely regarded as uneconomical. The present research is predicated on the assumption that an economically feasible separation requires a continuous, electrokinetic separation procedure.Solid-liquid separation represents a significant problem for the phosphate mining industry The waste suspensions, initially containing 3-5 wt% solids, are pumped to large impoundment areas termed clay settling ponds. When incorporated, the addition of flocculating agents produce a rapid, but partial, separation, to approximately 10 wt% solids. A further increase in solids content proceeds very slowly. Hindered settling, followed by self-weight consolidation, requires as much as 25 years to reach a solids content of 40 wt%. This is an important target value, because its shear strength will then allow the addition of a surcharge (typically a sand cap) to increase the consolidation rate and magnitude. Through a systematic development of prototypes, from batch to semi-continuous with emphasis on water clarification to semi-continuous with emphasis on solids extraction, our team has developed a fully continuous electrokinetic dewatering prototype. The system takes advantage of the charged nature of the suspended solids. When subjected to an applied electric field, the solids are attracted to the anode and clarified water is collected at the cathode. The process is capable of generating a 40 wt% clay cake and clarified water with turbidity levels below 1 NTU within hours rather than years. Optimization of the design was possible by developing a constitutive relationship between the final solids content, the applied electric field, and the residence time. Successful implementation of a continuous electrokinetic separation process will reduce the vast amount of water consumed by industry. While the process was developed for phosphatic clay suspensions, it is anticipated that electrokinetic dewatering may be applicable to other mining operations such as those associated with the oil sand tar tailings in Canada. This presentation will describe the current state of development, including energy and power requirements.

Development of Electrokinetic Dewatering for Phosphate Mine Tailings

Solid-liquid separation represents a significant problem for the phosphate mining industry. A dilute suspension of phosphatic clays is a waste product of the phosphate ore beneficiation (mineral processing). The suspensions, containing initially 3-5 wt% solids, are pumped to large impoundment areas termed clay settling areas. Addition of flocculating agents causes a rapid but partial separation, resulting in a suspension containing roughly 10 wt% solids. Further increase in solids content, however, proceeds very slowly. Hindered settling and self-consolidation of clay requires as much as 25 years to reach a solids content of 40 wt%. In central Florida, clay settling areas cover over 150 square miles, representing 30% of the mined land.Discovery of new exploitable phosphate ore deposits in Florida, coupled with increased environmental awareness as reflected by regulatory agencies, has motivated a search for a technology that can achieve rapid and economic separation of solids from water. The use of an applied electric field for dewatering was explored in the late 1990s. Electrokinetic separation was found to be promising, but the technology was not considered economical.Under funding from Mosaic, a major phosphate mining company, our group produced bench-top results similar to those reported in the literature. Using a large number of experimental results, we then identified constitutive relations among the increase in solids content, the electric field, and the elapsed time. The analysis showed that for short times, an increase in solids content could be achieved at any electric field, but the maximum increase depended on the strength of the electric field. The constitutive relation was used in boundary element simulations for application of electrokinetic separation to an existing clay settling area. The energy costs were found to be acceptable, but the power requirement was prohibitive.We turned then to development of a fully continuous electrokinetic separation device that could be used as a process unit for a beneficiation plant. This development was stepwise. A semi-continuous system was designed for continuous removal of supernatant water. Under pseudo-steady-state operation, low-turbidity water (<10 NTU) was separated from a clay solids suspension by a combination of electrokinetic dewatering and gravity settling.A second semi-continuous system, which introduced a rotating belt between electrodes to facilitate removal of clay sludge, was designed and tested. A series of small-scale batch experiments were used to identify the optimal belt properties. A constitutive relation similar to that developed for batch operations showed that this system had greater efficiency. This equipment produced thickened clay cake with a solids content greater than 33 wt%. The information obtained from the semi-continuous prototypes was used to design a fully continuous system which provides both clear water and thickened clay.The academic team working on the development includes chemical, mechanical, and civil engineers. The approach taken can be characterized as application of fundamental engineering science to a practical problem of great societal importance.

Laboratory-Scale Apparatus for Semi-Continuous Electrokinetic Dewatering of Phosphatic Clay Suspensions

The by-products of phosphatic clay suspensions are a major waste product of the phosphate mining industry. The phosphate clay suspensions produced from beneficiation are about 130,000 gallons per minute (GPM) at about a solids content of 2 wt%. After flocculation the settled clay suspensions at 10% solids content are pumped into the clay settling areas (CSAs) for natural settling. This natural clay settling process takes as much as 25 years to reach the demanded value of 40 wt% solids content. Therefore, the CSAs are frequently constructed on the unmined land and currently cover an area of over 100,000 acres in Florida. Disposal of the phosphatic clay suspensions has become the phosphate mining industry’s major challenge. Thus, it is necessary to develop a technique to increase the solids content of the effluent of phosphate clay suspensions from a phosphate mining beneficiation plant and thereby can save the land used for CSAs and recycling water. A semi-continuous electrokinetic dewatering apparatus for phosphatic clay suspensions has been designed and its performance has been evaluated. A 23 factorial design was applied to determine the optimum process parameters. The results show that the electric field was found to have the greatest positive influence on the solids content. The maximum change in solids content reached a plateau as a function of operating time at a given electric field. Moreover, the plateau occurred earlier at larger electric fields, indicating that for the maximum solids content the optimum parameters of the electric field and the operating time can be determined. The CEDA had lower energy consumption and continuously produced the thickened clay which had the highest solid content of about 33 wt%. The CEDA can be operated to cope with dilute initial solids content (3-10%) from a phosphate mining beneficiation plant. The CEDA has potential to replace existing thickening equipment.

Evolutionary Development for Electrokinetic Dewatering of Phosphate Mine Tailings

The processing and storage of phosphatic clay suspensions (or mine tailings) which result as a waste product from phosphate mining industry represent an important economic and environmental problem. A very long time is required to allow gravity-driven settling of clay suspensions with an initial 2-3 wt% solids content, and decades may be required to reach 25-30 wt% solids content. The associated impoundments occupy over 100 square miles of land in Florida alone.A combination of experimental and modeling approaches were used to explore the use of imposed electric fields to achieve electrokinetic separation. Batch experiments were used to guide the development of a constitutive relationship describing the changes in solids content with time (t) and applied electric field (E)1,2. A linear behavior between final solids content and Et was found in at short times, and the upper limit of separation was controlled by the value of electric field only.Subsequently, a semi-continuous system was designed for continuous removal of supernatant water. This system allowed measurement of supernatant turbidity, pH, and changes in solids content as functions of applied electric field, flow rate, and settling time. Under pseudo-steady-state operation, low-turbidity water was separated from a clay solids suspension by a combination of electrokinetic dewatering and free settling. A semi-continuous system, which introduced a rotating belt between electrodes to facilitate removing clay sludge, was designed and tested. The batch experiment set up was used to optimize fabric selection. This equipment was able to continuously producing thickened clay cake with a solids content of up to 33 wt%. Evaluation of parameters including electrode spacing, electric field, and residence time provided an understanding of the path for optimization. A similiar constitutive relationship as in batch experiment was also estanblished which correlates final solids content to electric field and residence time.All the systems were also evaluated from an econonic perspective. The energy requirement of the semi-continuous operation that facilitated sludge removal had a lower energy requirement value at a given electric field as compared with the result from batch experiments and the previous semi-continuous operation. All systems followed the trend that high electric fields have a high energy requirement. References J.P. McKinney, M.E. Orazem, A constitutive relationship for electrokinetic dewatering of phosphatic clay slurries, Miner. Metall. Process. 28 (2011) 49.J.P. McKinney, M.E. Orazem, Electrokinetic dewatering phosphatic clay settling areas: numerical simulation and economic assessment, Miner. Metall. Process. 28 (2011) 71.

Exploring the challenges associated with the greening of supply chains in the South African manganese and phosphate mining industry

As with most mining activities, the mining of manganese and phosphate has serious consequences for the environment. Despite a largely adequate and progressive framework for environmental governance developed since 1994, few mines have integrated systems into their supply chain processes to minimise environmental risks and ensure the achievement of acceptable standards. Indeed, few mines have been able to implement green supply chain management (GrSCM). The purpose of this article was to explore challenges related to the implementation of GrSCM and to provide insight into how GrSCM can be implemented in the South African manganese and phosphate industry. This article reported findings of a qualitative study involving interviews with 12 participants from the manganese and phosphate industry in South Africa. Purposive sampling techniques were used. Emerging from the study were six themes, all of which were identified as key challenges in the implementation of GrSCM in the manganese and phosphate mining industry. From the findings, these challenges include the operationalisation of environmental issues, lack of collaboration and knowledge sharing, proper application of monitoring and control systems,lack of clear policy and legislative direction, the cost of implementing GrSCM practices, and the need for strong leadership and management of change. On the basis of the literature reviewed and empirical findings, conclusions were drawn and policy and management recommendations were accordingly made.

Electrokinetic Methods For Dewatering Of Phosphatic Clay Slurries

Phosphatic clay slurries constitute a waste product of the Florida phosphate mining industry. The clay slurries currently occupy as much as 40% of the land that has been mined. Water removal from the clays greatly reduces the amount of land they occupy. Application of an electric field is demonstrated as an approach to increase the rate of water removal from the clays. A set of benchtop experiments was used to develop parameters that could be used for design of a water removal system. A design equation was established which predicts the time required for the clays to reach an acceptable solids content as a function of the applied electric field. A mathematical model CP3D, developed at the University of Florida, was used to simulate different electrode configurations in a large-scale clay settling pond. This comparison illustrated the effects of design on energy efficiency and the behavior of the electric field.

Characterization of aqueous lead removal by phosphatic clay: Equilibrium and kinetic studies

Immobilization of heavy metals from contaminated environments is an emerging field of interest from both resource conservation and environmental remediation points of view. This study investigated the feasibility of using phosphatic clay, a waste by-product of the phosphate mining industry, as an effective sorbent for Pb from aqueous effluents. The major parameters controlling aqueous Pb removal, viz. initial metal ion concentrations, solution pH, sorbent amounts, ionic strength and presence of both inorganic and organic ligands were evaluated using batch experiments. Results demonstrated that aqueous Pb removal efficiency of phosphatic clay is controlled mainly by dissolution of phosphatic clay associated fluoroapatite [Ca 10(PO 4) 5CaCO 3(F,Cl,OH) 2], followed by subsequent precipitation of geochemically stable pyromorphite [Pb 10(PO 4) 6(F,Cl,OH) 2], which was confirmed by both X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis. Lead removal efficiency of phosphatic clay increased with increasing pH, sorbent amount and decreasing ionic strength. It also depends on the nature of complexing ligands. Formation of insoluble calcium oxalate and lead oxalate in the presence of oxalic acid explained high uptake of Pb by phosphatic clay from aqueous solution. However, Pb sorption kinetics onto phosphatic clay were biphasic, with initially fast reactions followed by slow and continuous Pb removal reactions. The slow reactions may include surface sorption, co-precipitation and diffusion. The exceptional capability of phosphatic clay to remove aqueous Pb demonstrated its potential as a cost effective way to remediate Pb-contaminated water, soils and sediments.

Heavy metal interactions with phosphatic clay: sorption and desorption behavior.

Heavy metals produced and released during agricultural and industrial activities may pose a serious threat to the environment. This study investigated the effectiveness of phosphatic clay, a by-product of the phosphate mining industry, for immobilizing heavy metals (Pb(+2), Cd(+2), and Zn(+2)) from aqueous solutions. A batch equilibrium technique was adopted to evaluate metal sorption in the presence of 0.05 M KNO3 background electrolyte solution. The amounts of metals sorbed onto phosphatic clay decreased in the order Pb(+2) > Cd(+2) > Zn(+2). Desorption data suggest that a large fraction of metals sorbed onto phosphatic clay stayed intact under a wide variation in extracting solution pH (ranging from 3 to 10). Desorption rates were slowest for Pb followed by Cd and Zn. Only 8.1 to 23.1% of Pb, 8.4 to 45% of Cd, and 21.9 to 73.9% of Zn sorbed on phosphatic clay was mobilized by USEPA toxicity characteristic leaching procedure (TCLP) solutions at pH 2.93+/-0.05 and 4.93+/-0.05, respectively. Formation of fluoropyromorphite [Pb10(PO4)6(F2)], confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), after reaction of aqueous Pb with phosphatic clay suggested that precipitation remained the dominant mechanism for Pb removal from aqueous solution. In the case of aqueous Cd and Zn interaction with phosphatic clay, we are not able to confirm the formation of a new amorphous and/or crystalline phase on the basis of available information. Other possible sorption mechanisms for Cd and Zn may include sorption and coprecipitation. Thus, phosphatic clay may be an effective amendment for in situ immobilization of heavy metals in contaminated soils and sediments.

Challenging the “Crago” double float process II. Amine-fatty acid flotation of siliceous phosphates

In the conventional phosphate flotation (Crago) process, 30–40% by weight of the silica present in the feed are floated twice, first by fatty acid, and then by amine. The Crago process is therefore inefficient in terms of collector efficiency. Also, the phosphate mining industry is faced with higher fatty acid prices, lower feed grade, and stricter environmental regulations. For these reasons, the Florida Institute of Phosphate Research has developed an amine fatty acid flotation flowsheet, the reverse “Crago”. In this process, fine sands are first floated with a minimum dosage of amine condensate added stepwise. The concentrate from prefloat is then floated with a blend of surfactant/fatty acid/fuel oil. The technical and economic feasibility of this process were evaluated on seven feeds of varying characteristics, producing concentrates analyzing 30–32% P 20 5 and 4–10% Insol with P 20 5 recoveries of over 93%, at total reagent costs below $2 per ton of concentrate. This novel process could simplify the current processing fiowsheet by eliminating the acid scrubbing circuit, reducing the sizing section, and reducing the number of conditioners. The process consumes about one third to half the amount of reagents required by the Crago process at significantly improved flotation recovery. The effect of slimes (in either the flotation feed or water) and techniques for reducing this effect were also investigated.