Limonitic Laterite Ore Research Articles

Reducibility of nickeliferous limonitic laterite ore from Central Anatolia

Limonitic nickel laterite from Sivrihisar reserve in Turkey was reduced at 700–1100°C by the addition of 5·74, 8·61 and 11·48 wt-% coal under an argon atmosphere. The run-of-mine ore and the reduced samples were studied using X-ray diffraction. The metallisation of Fe was found to be limited up to 900°C, but increased rapidly at higher temperatures. The metallisation of Ni and Co increased when the temperature was increased from 700 to 800°C, almost levelled off up to 900°C and then increased up to 1100°C. The results also showed that increased coal additions did not affect Fe metallisation up to 900°C. At 1000°C the metallisation of Fe became slightly better, but its effect was more pronounced at 1100°C. The increased coal addition affected the nickel reduction equally at all temperatures, while it had no effect on the metallisation of Co.La réserve de nickel limnétique en Turquie a été réduit à 700-1100 ° C par l'addition de 5.74, 8.61 and 11.48 wt-% de charbon sous atmosphère d'argon. Le minerai et les échantillons réduits ont été étudiés par DRX. La métallisation de Fe a été jugée limitée à 900 ° C, mais elle a augmenté rapidement à des températures plus élevées. La métallisation de Ni et Co a augmenté lorsque la température a été augmentée de 700 à 800 ° C, presque stabilisé jusqu'à 900 ° C puis 1100 ° C. Les résultats ont également montré que l'augmentation des ajouts de charbon n'a pas affecté Fe métallisation jusqu'à 900° C. A 1000 ° C, la métallisation de Fe s'est un peu ameliorée, mais son effet était plus prononcé à 1100 ° C. L'augmentation du taux de charbon a affecté une constante réduction de nickel à toutes les températures, alors qu'il n'a eu aucun effet sur la métallisation de Co.

Thermodynamic analysis of the Fe–Ni–Co–Mg–Si–O–H–S–C–Cl system for selective sulphidation of a nickeliferous limonitic laterite ore

An increasing percentage of nickel is being extracted from the laterite ores for which there exists considerable potential for new process development. In the current research, a thermodynamic analysis of the Fe–Ni–Co–Mg–Si–O–H–S–C–Cl system has been performed in order to establish the possible sulphidation conditions for the upgrading of a limonitic laterite ore. The study was performed using the equilibrium module of HSC Chemistry® 6.1, and the data available in the literature were utilised to determine the activity coefficients of the various species employed in the calculations. The effects of variables such as temperature, amount of sulphur and carbon and chlorine additions on both the nickel grade and recovery in the monosulphide solid solution (mss) were determined. Alternative sulphidizing agents were also considered. Nickel recoveries of about 85% could be achieved at a grade of 10% nickel in the mss. Limiting factors in the sulphidation process were the formation of iron sulphide (FeS) and the relatively high stability of nickel oxide in the nickel ferrite (NiFe2O4), in comparison to the other phases, which resulted in excessive sulphur requirements of over 100kg of S/tonne of ore. Methods to overcome these restrictions were discussed and the thermodynamic results were compared to the published experimental values.

Selective pressure leaching of Fe (II)-rich limonitic laterite ores from Indonesia using nitric acid

The selective extraction of nickel and cobalt over iron from an Indonesian limonitic laterite was investigated using nitric acid pressure leaching (NAPL). The mineralogical analysis showed that the major minerals were goethite and magnetite, and the content of the divalent iron was as high as 7.06%. Nickel and cobalt were mainly distributed in these two minerals; however, the distribution was non-uniform. A series experiments were conducted to examine the basic parameters and propose the optimal conditions for the extraction. When the ore was treated via HPAL under the optimal condition, the extracted nickel and cobalt were less than 75%, and the iron concentration in the leach liquor was over 12.5g/L. By contrast, over 85% of nickel and cobalt were extracted and about 1.8g/L iron was achieved using NAPL. The loss of nickel and cobalt can be mainly attributed to the undissolved magnetite and manganese minerals. The leaching process of NAPL is a dissolution–oxidation–precipitation mechanism, and in this process nitric acid acts as both a lixiviant and an oxidant. The formation of hematite results in a low iron concentration in the leach liquor without oxygen injected. Meanwhile, the oxidation and the precipitation of dissolved divalent iron results in a calculated savings in acid consumption of about 120kg nitric acid per ton of ore can be obtained, which is equal to over 93kg of sulfuric acid per ton of ore. Moreover, lower residual acid (20g/L nitric acid) is a significant advantage of NAPL. The iron residues had a high iron content (>56wt%) with no sulfur, making it suitable as raw materials for ironmaking.

Selective Leaching Nickel from the Pre-Reduced Limonitic Laterite Ore at Atmospheric Pressure

In this paper a novel method for selective leaching nickel from pre-reduced laterite ore at atmospheric pressure was reported. The reduced calcine was leached in thin acid liquor to liberate the nickel and iron together firstly. By properly controlling the leaching condition, the leached iron ion could hydrolyze as goethite precipitate and regenerate the acid consumed in the leaching procedure. Finally, the nickel is selectively extracted into the leaching solution. The main factors in the leaching process, such as reduction degree of the laterite ore, acidity of the leaching solution were investigated as influence on the nickel extraction. The test results showed that selectively leaching of nickel could be achieved with an extraction degree up to 90% by reducing most of the iron in the lateritic ore to wuestite and controlling the pH value of the leaching solution below 2.5.

Pressure Leaching of Limonitic Laterite Ores in H<sub>2</sub>SO<sub>4</sub>-Mg(NO<sub>3</sub>)<sub>2</sub> Medium

A limonitic laterite ore from Indonesea was treated by pressure leaching in H2SO4-Mg(NO3)2 medium, using Mg(NO3)2 as an oxidant. Experiments were conducted in order to determine the optimum conditions by studying various parameters, including Mg(NO3)2/ore mass ratio, initial acidity, reaction temperature, holding time and liquid/solid ratio. Pressure leaching experiments showed that nickel, cobalt and iron extractions were 90.8 %, 91.9 % and 2.1 % after 60 min of leaching at 493 K with 0.06 g/g Mg(NO3)2/ore mass ratio, 140 g/L initial acidity and 2 mL/g liquid/solid ratio.The total decrement of acid consumption was 72 g H2SO4/kg ore in the presence of Mg(NO3)2.

Activation pretreatment of limonitic laterite ores by alkali-roasting using NaOH

Activation pretreatment of Cr-containing limonitic laterite ores by NaOH roasting to remove Cr, Al, and Si, as well as its effect on Ni and Co extraction in the subsequent pressure acid leaching process was investigated. Characterization results of X-ray diffraction (XRD) and scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/XEDS) show that goethite is the major Ni-bearing mineral, and chromite is the minor one. Experimental results show that the leaching rates of Cr, Al, and Si are 95.6wt%, 83.8wt%, and 40.1wt%, respectively, under the optimal alkali-roasting conditions. Compared with the direct pressure acid leaching of laterite ores, the leaching rates of Ni and Co increase from 80.1wt% to 96.9wt% and 70.2wt% to 95.1wt% after pretreatment, respectively. Meanwhile, the grade of acid leaching iron residues increases from 54.4wt% to 62.5wt%, and these residues with low Cr content are more suitable raw materials for iron making.

Reductive acid leaching of laterite and metal oxides — A review with new data for Fe(Ni,Co)OOH and a limonitic ore

The reductive leaching of nickel laterite has attracted the interest of many researchers due to the enhanced kinetics of nickel and cobalt dissolution in the presence of acids and reducing agents during atmospheric, pressure, heap or bio leaching processes. Systematic studies on synthetic oxides and natural ores can shed light on the reaction mechanism and lead to investigations of beneficial reagents for further studies. This paper briefly reviews the literature and describes a comparative study of metal leaching from synthetic goethite spiked with nickel or cobalt and a limonitic laterite ore to rationalise the role of reducing agents in acid media. Results are discussed on the basis of the effect of speciation, surface chemical reactivity of oxides and heterogeneous kinetic models.

Dechromization Kinetics of Limonitic Laterite Ores by Alkali-Roasting Method Using Sodium Hydroxide

A novel process was proposed for the activation pretreatment of Cr-containing limonitic laterite ores by NaOH roasting. The dechromization kinetics of the laterite ores and the effect of particle size, NaOH-ore ratio, and roasting temperature on Cr extraction were studied in detail. Experimental results indicate that decreasing the particle size and increasing the NaOH-ore ratio and roasting temperature increase the Cr extraction rate. Approximately 96% Cr in the laterite ores could be extracted under the optimal alkali-roasting conditions. The results also indicate that the Avrami model is suitable for the dechromization process and that the apparent activation energy is calculated 11.12 kJ·mol-1. The 99.5% Cr2O3 was obtained from Na2CrO4 leached in the alkali solution by liquid-phase reduction and then calcining at high temperature.

Leaching of limonitic laterite ore by acidic thiosulfate solution

Cobalt is usually recovered as a by-product of copper and nickel processing, and only a small amount of cobalt is derived from laterites although a vast majority of cobalt resources in them. The exploitation of limonitic laterite containing high content of cobalt is becoming increasingly important. The mineralogy of a limonitic laterite ore was characterized by environmental scanning electron microscope (ESEM) and X-ray diffraction (XRD) in this paper. The results show that nickel occurs in goethite mainly, while cobalt is predominantly associated with manganiferous minerals. Thiosulfate is found to be able to selectively leach cobalt from limonitic laterite in the presence of sulfuric acid, and 91% Co, 22% Ni, 10% Fe are leached from an ore containing 0.13% Co, 1.03% Ni within the first 5 min at 90 °C under the conditions of 10 g/L sodium thiosulfate, 8% (w/w) sulfuric acid and 10:1 L/ S ratio. The leaching kinetics of Mn and Co by acidic sodium thiosulfate solution can be characterized by the Avrami equation. In acidic solution, thiosulfate readily decomposes into sulfur and sulfur dioxide as intermediary reagents to reduce pyrolusite (MnO 2) and goethite (FeOOH); therefore, nickel and cobalt associated with goethite and pyrolusite respectively are extracted due to reduction dissolution. Furthermore, cobalt is selectively leached over iron and nickel because pyrolusite is preferentially reduced by acidic thiosulfate rather than goethite. The novel process may give an alternative method to selectively recover cobalt as the primary product from limonitic laterites at atmospheric pressure.

Activation pretreatment of limonitic laterite ores by alkali-roasting method using sodium carbonate

Activation pretreatment of Cr-containing limonitic laterite ores by Na 2CO 3 roasting to remove Cr and Al, as well as its effect on Ni and Co extraction in the subsequent pressure acid leaching process were investigated. X-ray diffraction (XRD), thermogravimetric (TG), and scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/XEDS) techniques were used to characterize the laterite ores and the water leaching residues of alkali roasting and found that goethite is the major Ni-bearing mineral and chromite the minor one. Alkali-roasting pretreatment breaks the mineral lattices of the laterite, exposing their Ni and Co, which leads to higher extraction of these two metals under milder operation conditions in the subsequent pressure acid leaching process. Experimental results showed that the leaching of Cr and Al were up to 99 wt% and 80 wt%, respectively, under optimal alkali roasting and water leaching conditions. Compared with the direct pressure acid leaching of the raw laterite ores, leaching of Ni and Co increased from 79.96 wt% to 97.52 wt% and 70.02 wt% to 95.33 wt%, respectively, after alkali-roasting activation pretreatment was performed. Meanwhile, the grade of acid leaching iron residues increased from 55.31 wt% to 62.92 wt%, and these residues with low Cr content could be more suitable as the raw materials for iron-making.

Leaching behavior of metals from limonitic laterite ore by high pressure acid leaching

The leaching behavior of metals from a nickeliferous limonitic laterite ore was investigated by high pressure acid leaching process for the extraction of nickel and cobalt. The effects of sulfuric acid added, leaching temperature, leaching time and liquid/solid (L/S) ratio on metals extraction were examined. More than 97% Ni, 96% Co, 93% Mn, 95% Mg and less than 1% Fe are extracted under optimum conditions. Analysis of the high pressure acid leaching residue by chemical and XRD analysis indicates that the residual iron and sulfur are mainly present in phases of hematite and alunite, respectively. The high pressure leaching process provides a simple and efficient way for the high recovery of nickel and cobalt from laterite ore, leaving residue as a suitable iron resource.

Reductive dissolution of ferric iron minerals: A new approach for bio-processing nickel laterites

Nickel laterites represent the major ore reserves of this base metal present in the lithosphere. However, processing these ores by conventional technologies involves considerable energy or reagent expenditure and consequently is less cost-effective than extracting nickel from sulfide ores. Biological options, using metal-complexing organic acids and mineral acids generated by fungi and bacteria, have been investigated but generally found to be ineffective in terms of extraction dynamics or yields. We have examined the possibility of using bacteria that can bring about the reductive dissolution of ferric iron minerals and thereby facilitate the extraction of nickel from a lateritic ore at relatively low (<30–45 °C) temperatures. Four species of iron-reducing acidophilic bacteria were screened for their abilities to solubilise nickel from a limonitic laterite ore in which the major iron mineral present was goethite. One of these ( Acidithiobacillus ferrooxidans) was selected for further study only the basis of it being able to use a cost-effective energy source (elemental sulfur) to mediate the dissolution of goethite at mildly acidic conditions (pH < 2). Cultures were set up in 2 L bioreactors, maintained at pH 1.8 (±0.1) and 30 °C, and initially aerated (to promote growth of the bacteria on sulfur) and then switched to anaerobic conditions when nickel laterite ore (crushed to <6 mm, with a nickel grade of 0.5%) was added. Over 70% of the nickel present in the ore was solubilised within 14 days, and solubilised metals remained in solution due to the low pH of the leachate. In contrast, only 10% of the nickel was solubilised (by non-reductive acid dissolution) when the cultures were continuously aerated. The results suggest that biological processing of limonitic nickel laterites is technically feasible and, more generically, that reductive dissolution can be used to bioprocess ferric oxide mineral ores.

MICROWAVE DRYING OF NICKELIFEROUS LIMONITIC LATERITE ORES

Nickeliferous laterite ores contain large amounts of both free and combined water which are removed during processing for metal extraction. In this study, the application of microwaves for the drying of a briquetted nickeliferous limonitic laterite ore, was investigated. Microwave drying tests were performed at a frequency of 2460 MHz and the sample mass was continuously monitored in order to determine the drying rate. The variables investigated were sample mass, microwave power, briquette aspect ratio, specific surface area and compaction pressure. For comparison purposes, conventional drying tests were performed in the temperature range of 44 to 228°C. It was found that the microwave drying rates were two to three times higher than the conventional drying rates. This was attributed to the inverse temperature gradient with microwave heating which promoted enhanced mass transfer of the water.Les minerais nickélifères de latérite contiennent de grandes quantités d’eau tant à l’état libre que combinées qui sont enlevées lors du traitement d’extraction du métal. Dans cette étude, on a investigué l’utilisation des micro-ondes pour le séchage d’un minerai nickélifère briqueté de latérite limonitique. On a effectué des essais de séchage par micro-ondes à une fréquence de 2460 MHz alors que la masse de l’échantillon était continuellement surveillée afin de déterminer le taux de séchage. Les variables étudiées incluaient la masse de l’échantillon, la puissance du micro-onde, le rapport longueur/diamètre de la briquette, la surface spécifique et la pression de compaction. Pour le but de comparaison, on a effectué des essais de séchage conventionnel dans la gamme de température de 44 à 228°C. On a trouvé que les taux de séchage par micro-ondes étaient deux ou trois fois plus élevés que les taux de séchage conventionnel. Ceci était attribué au gradient inverse de température du chauffage par micro-ondes qui favorisait un transfert amélioré de la masse d’eau.

Microwave heating behaviour of nickeliferous limonitic laterite ores

The nickeliferous laterite ores, in which the nickel occurs in oxide form, represent a significant potential resource of metallic nickel. However, in comparison to the nickel-containing sulfide ores, the extraction costs are relatively high and thus it will be necessary to develop new processing techniques, which are both technically and economically viable. In the present research, the potential application of microwaves for the heating of a nickeliferous limonitic laterite ore ((Fe,Ni)O(OH) · nH2O) was investigated. Firstly, since the nickeliferous limonitic laterite ore contains considerable moisture, both free and combined, then thermogravimetric analysis (TGA) was performed in order to characterize the changes, which result from the dehydration processes. Derivative thermogravimetric analysis (DTGA) curves were calculated from the TGA data. Secondly, the real (ε′) and imaginary (ε″) permittivities of the ore were measured at frequencies of 912 and 2460 MHz at temperatures up to about 1000 °C using the cavity perturbation technique and these results were related to the DTGA curves. Also, the loss tangent (tanδ=ε″/ε′) was calculated from the permittivity data. Finally, the microwave heating behaviour of the nickeliferous limonitic laterite ore was determined at 2460 MHz. The results show that the both the real (ε′) and imaginary permittivities (ε″) and the loss tangent (tanδ) increase with temperature and change as both the free and the combined moisture are removed. The permittivities (ε′ and ε″) increased with increasing slope of the TGA curve and vice versa during the goethite to hematite dehydroxylation reaction, where there was a maximum in the permittivities (ε′ and ε″). It is proposed that these changes, which occur during the dehydroxylation reaction, are a result of the liberation of hydroxyl units from the goethite structure. Furthermore, some hydroxyl units were retained in the hematite structure (i.e. hydrohematite (α-Fe2−x/3O3−xOHx)) even after the goethite to hematite transition and thus the permittivities of the dehydroxylated ore were higher than that of normal hematite. With regards, to their microwave heating behaviour, it is shown that despite the relatively low permittivities (ε′ and ε″) of these materials at low temperatures, they can be heated using microwaves. The microwave heating process can be improved by conventional preheating of the sample or by the addition of charcoal as a susceptor or by selecting a crucible material, which acts as a susceptor. There is a rapid increase in the permittivities over the temperature range of about 600–800 °C and this combined with the low thermal conductivities of these oxides, can result in rapid internal heating of the sample and thermal runaway.

Microwave heating behaviour of nickeliferous limonitic laterite ores

The nickeliferous laterite ores, in which the nickel occurs in oxide form, represent a significant potential resource of metallic nickel. However, in comparison to the nickel-containing sulfide ores, the extraction costs are relatively high and thus it will be necessary to develop new processing techniques, which are both technically and economically viable. In the present research, the potential application of microwaves for the heating of a nickeliferous limonitic laterite ore ((Fe,Ni)O(OH) · nH 2O) was investigated. Firstly, since the nickeliferous limonitic laterite ore contains considerable moisture, both free and combined, then thermogravimetric analysis (TGA) was performed in order to characterize the changes, which result from the dehydration processes. Derivative thermogravimetric analysis (DTGA) curves were calculated from the TGA data. Secondly, the real ( ε ′) and imaginary ( ε ″) permittivities of the ore were measured at frequencies of 912 and 2460 MHz at temperatures up to about 1000 °C using the cavity perturbation technique and these results were related to the DTGA curves. Also, the loss tangent (tan δ= ε ″/ ε ′) was calculated from the permittivity data. Finally, the microwave heating behaviour of the nickeliferous limonitic laterite ore was determined at 2460 MHz. The results show that the both the real ( ε ′) and imaginary permittivities ( ε ″) and the loss tangent (tan δ) increase with temperature and change as both the free and the combined moisture are removed. The permittivities ( ε ′ and ε ″) increased with increasing slope of the TGA curve and vice versa during the goethite to hematite dehydroxylation reaction, where there was a maximum in the permittivities ( ε ′ and ε ″). It is proposed that these changes, which occur during the dehydroxylation reaction, are a result of the liberation of hydroxyl units from the goethite structure. Furthermore, some hydroxyl units were retained in the hematite structure (i.e. hydrohematite (α-Fe 2− x/3 O 3− x OH x )) even after the goethite to hematite transition and thus the permittivities of the dehydroxylated ore were higher than that of normal hematite. With regards, to their microwave heating behaviour, it is shown that despite the relatively low permittivities ( ε ′ and ε ″) of these materials at low temperatures, they can be heated using microwaves. The microwave heating process can be improved by conventional preheating of the sample or by the addition of charcoal as a susceptor or by selecting a crucible material, which acts as a susceptor. There is a rapid increase in the permittivities over the temperature range of about 600–800 °C and this combined with the low thermal conductivities of these oxides, can result in rapid internal heating of the sample and thermal runaway.

A surface reaction kinetic model to compare the reductive leaching of iron from goethite, magnetite, and limonitic nickel laterite ores by acidic sulfur dioxide

A surface reaction kinetic model to compare the reductive leaching of iron from goethite, magnetite, and limonitic nickel laterite ores by acidic sulfur dioxide

A comparative study of leaching kinetics of limonitic laterite and synthetic iron oxides in sulfuric acid containing sulfur dioxide

Limonitic laterite ore of particle size 90–125 μm containing goethite, magnetite and hematite was leached for 6 h at a pulp density of 10% (wt/vol) in sulfuric acid in the absence or presence of sulfur dioxide at atmospheric pressure and 90 °C in a glass reactor vessel. The sulfur dioxide flow rate was kept at 0.6 L min −1 L −1 of slurry to maintain a constant SO 2 concentration of ≈0.3 mol L −1 in solution, and the sulfuric acid concentration was varied between 0 and 0.72 mol L −1. The relative percentage extractions of Fe, Ni, Co and Mn indicate that the Fe and Ni extractions are inter-related at a ratio of Ni/Fe=0.7–0.9 and suggest the possibility of catalysis of manganese dissolution by solubilized iron(II). This leads to a Mn extraction of over 90% in less than 30 min compared with 20–40% Fe extraction in the same period, depending on the acid concentration. The initial rate of leaching of iron shows first-order dependence with respect to H +. Whilst the synthetic iron oxides leach according to the shrinking particle/sphere kinetic model, the results obtained in the first 4 h of laterite leaching can be described by a shrinking particle model with an insoluble product layer that retards the diffusion of H + to the reaction sites at the interface. The heterogeneous rate constants for both models increase with the increase in H + concentration. The effective diffusion coefficient of H + (D H +) through the product layer (0.5×10 −9 to 4×10 −9 cm 2 s −1), determined in the present study, is in the magnitude range of the reported data for D H + in polycrystalline Fe 3O 4 and MnO 2, but lower than D H + in aqueous media, 9×10 −5 cm 2 s −1.

Drying kinetics of nickeliferous limonitic laterite ores

The drying kinetics of a nickeliferous limonitic laterite ore were investigated in the temperature range of 44–228 °C, using a thermogravimetric technique, and the results were characteristic of a non-hygroscopic porous solid. For drying temperatures below 100 °C, the drying rate curves exhibited three stages: a relatively short incubation or set-up period, a constant rate drying period and a decelerating rate drying period. At temperatures above the boiling point of water, there was no constant rate drying period and only the incubation and the decelerating rate stages were observed. The graphical critical moisture fraction, X Cr , which is the moisture content at which the transition from the constant rate period to the decelerating rate period occurs, was found to be 0.064 and was independent of the drying temperature and thus the drying rate. Using the concepts of the relative drying rate ( f) and the characteristic moisture content ( Φ), a characteristic drying curve was determined for the ore. The drying kinetics, when the sample had attained the equilibrium temperature, exhibited non-Arrhenian behavior and the drying process was approximated using two linear relationships. The activation energies over the two temperature ranges were determined to be as follows: 25.5 kJ/ mole 44 ° C⩽T⩽100 ° C 12.9 kJ/ mole 100 ° C⩽T⩽228 ° C The activation energies were both relatively low and this indicates that the process was diffusion controlled in both temperature regimes. It is postulated that at temperatures below 100 °C, the rate-determining step was attributed to boundary layer control while at higher temperatures the rate-determining step was internal diffusion control. Effective diffusion coefficients ( D e) were calculated from the drying rate data and they varied with both concentration and temperature. At low moisture contents, a maximum was observed in the effective diffusion coefficient and this was explained in terms of a maximum in the vapour phase diffusivity at low moisture contents. At temperatures below the boiling point of water, the plateau at the maximum was extended and the diffusion coefficient was relatively constant over the concentration range X=0.02 –0.055. The maximum in the diffusion coefficient was found to vary with temperature as T n , where n=1.8.

Scale formation in a batch reactor under pressure acid leaching of a limonitic laterite

The formation of scale under sulphuric acid pressure leaching conditions of a limonitic laterite ore was investigated. Experiments were conducted using a batch titanium autoclave in order to study the effects of acidity (0.15–0.40 M), and temperature (250–270°C) on scale formation. It was found that scale increases with acidity reaching a maximum at 0.22 M free sulphuric acid. Further increase of acidity causes reduction of scale, but scale is not affected by temperature. The scale mainly consists of hematite with traces of hydronium alunite as revealed by SEM photographs and EDX analyses. Anionic surfactants were tested as a means of scale reduction with some success. A reduction of 37% in scale formation was achieved at an acidity of 0.22 M and 270°C.