Dilute Sulphuric Acid Solution Research Articles

Leaching of Waste Pharmaceutical Blister Package Aluminium in Sulphuric Acid Media

In this study, the leaching behaviour of aluminium from waste pharmaceutical blister packages (WPBs) is investigated in sulphuric acid media to build future strategies for aluminium recycling from this non-recycled waste fraction. The results suggest that in hydrometallurgical recycling, passivation of aluminium during leaching can be mitigated in dilute sulphuric acid solutions (0.25 M), at high temperatures (60–80 °C) and specifically with H2O2 addition. With this system, 100% extraction was achieved within five hours under optimized conditions (H2SO4 = 0.25 M, T = 80 °C, H2O2 = 1.25 vol.%). The leaching mechanism is suggested to be based on electrochemical dissolution of metallic aluminium oxidized by H+ or H2O2, followed by fast passivation by Al2O3 and consequent chemical dissolution of Al2O3 at slower kinetics. The calculated activation energy (~69 kJ/mol) suggests that the leaching reaction is controlled by the chemical or electrochemical reaction step rather than diffusion. By WPB leaching, an aluminium sulphate solution could be obtained, suitable for further aluminium sulphate crystallization. This may provide a potential route for the valorisation of aluminium from a currently overlooked waste fraction of pharmaceutical blister packages.

Pitting corrosion on highly alloyed stainless steels in dilute sulphuric acid containing sodium chloride

Stainless steels are widely used in industrial assets and equipment. Despite their good corrosion resistance under a wide range of operating conditions, there is the possibility of pitting corrosion in the presence of chlorides. However, very few studies have identified the safe operating conditions for various high-alloyed stainless steel grades by comparing their pitting susceptibility. In this research, the susceptibility to pitting attack of five stainless steels with austenitic and duplex microstructures was examined in dilute sulphuric acid solution with varying amounts of NaCl at the temperatures of 50, 90 and 130°C. Based on potentiodynamic polarization scans, none of the test materials underwent pitting corrosion at 50°C, but differences in susceptibility to pitting attack were clear between the test materials and NaCl concentrations at the temperature of 90°C, and further temperature increase facilitated uniform corrosion. 28-day immersion tests at 90°C confirmed the pitting susceptibility of duplex grades 1.4662 (PREN 33) and 1.4462 (PREN 35) in the presence of at least 2000 mg/L NaCl, but not the susceptibility of a corresponding austenitic grade 1.4539 (PREN 34). The grades 1.4547 (PREN 43) and 1.4410 (PREN 44) were not susceptible to pitting corrosion under any of the studied conditions. The results from materials microstructural and electrochemical characterization are presented and discussed in this paper.

Determination of optimum conditions for maximum bioethanol yield from the Nigerian sweet potato (Ipomoea Batatas (L.) Lam)

Bioethanol is an important biofuel produced from biomass and is generally regarded as the future of fuels. This research was carried out for the main purpose of determining the optimum process conditions required for maximum bioethanol yield from the pulp of local sweet potato. The variety of potato used in this research is the Nigerian sweet potato (Ipomoea Batatas (L.) Lam) containing high amount of starch and the experiment was carried out with the use of Baker’s Yeast (Saccharomyces cerevisae) as the biocatalyst. In this study, the effect of acid concentration for hydrolysis, pH and fermentation period was examined. The sweet potato pulp was hydrolyzed using dilute sulphuric acid solutions of 0.5M, 1.5M and 2.5M and heated for 30 minutes at 100 ℃ yielding 0.9% (v/v) reducing sugar for fermentation. The hydrolysates were then subjected to fermentation at different pH values for different fermentation periods of 2, 3.5 and 5 days respectively. The pH values ranged from 4.5 to 6.5, an increment of 1.0 was used during the examination of pH with 1.0 M sodium hydroxide solution (NaOH) used for adjustment. The rate of bioethanol production was seen to increase as the pH and fermentation periods increased with the exception of the fermenting cultures of pH of 6.5. The maximum bioethanol yield of 13.40 ml, equivalent to 3.350% (v/v), was gotten from the hydrolysate obtained using the dilute acid of concentration 0.5M and left to ferment for 5 days at a pH of 5.5.

Data on the corrosion Inhibition Property of Rosemary on High Carbon Steel in dilute sulphuric acid, citric acid and sodium chloride solution

The data of electrochemical analysis of Rosmarinus officinalis (RO) essential oil effect on high carbon steel (HCS) in three different corrosive environment of sodium chloride, sulphuric acid and citric acid solution was achieved via weight loss method. Results revealed that Rosmarinus officinalis (RO) organic compound performed excellent well on high carbon steel samples with the optimum inhibition value occurring in NaCl solution with 97.87% after 504 h. The corrosion rate values were significantly high at 0 ml RO organic compound for all the three (3) corrosive environments as the time of immersion moves down to 504 h. It was clearly observed that time of immersion and concentrations of RO are the main determinant factor for the excellent adsorption performance of RO organic compound within the range of 504 h. Also, Rosmarinus officinalis (RO) organic compound retarded the severe corrosion rate of high carbon steel samples in other corrosive solutions with average range inhibition values between 40 and 78% after 504 h.

HIGH PERFORMANCE CONCRETE HAVING SILICA FUME AND METAKAOLIN AS A LIMITED REPLACEMENT OF CEMENT

The reason for this investigation is to create HPC using locally accessible ingredients in Pakistan. The trial study incorporates the utilization of silica fume and Metakaolin mostly. The mixture of preliminaries is made utilizing various volumes of the local supplementary cementitious materials SCM and aggregates to deliver HPC. Different tests are carried out, for example, compressive strength, Rapid chloride Penetration test and Concrete cured in dilute sulphuric acid solution are assessed. The water to cement proportion was kept as .5. Every concrete samples have 0, 5, 10, 15 and 20 percent cement replacing with metakaolin and silica fume halfway. The compression strength tests are done on 28 and 90 days of cured specimens. The rapid chloride permeability test and compressive strength on the concrete cylinder when place in dilute sulphuric acid solution is done after 28 days. The outcomes appeared by utilizing MK and SF in concrete improves the mechanical properties of the concrete with different degrees up to some level. The compressive quality of the concrete cylinder is maxed on 15% cement replacing with SCM. At 5% MK and SF cement replacement the strength of the concrete samples cured in dilute H2SO4 after 28 days shows rising in the result and its strength decreases at 10% cement replacement with SCMs than its strength increased again and gives max compressive strength with 15% replacement then strength reduces again at 20% cement additional with MK and SF moderately. The charge passing rate is maxed for normal concrete samples of RCPT. There is an inverse relationship between the charge passage and cement replacement. The Charge passage is decreased by increasing the quantity of cement additional with SCMs. 20% cement additional has the least charge level and is the best mix among all.

Corrosion Behaviour of 316L Stainless Steel in Hot Dilute Sulphuric Acid Solution with Sulphate and NaCl

The corrosion behaviour of 316L stainless steel (316L SS) in 10% H2SO4 solution (94°C) with various concentrations of NaCl (0–0.085 mol/L) was studied by immersion corrosion test and polarization methods, combined with SEM/EDS, XPS and XRD tests. The influence of NaCl on the corrosion of 316L SS was investigated. The results showed that at lower NaCl contents (0–0.0085 mol/L), the steel presented a general corrosion characteristic with a higher corrosion speed and the corrosion rate increased with the NaCl content. At higher NaCl contents (≥0.017 mol/L), the corrosion rate decreased remarkably due to the protective corrosion products precipitation which contained metallic sulphates and NaHSO4. However, the higher concentration of chloride ions caused micron pitting-like local dissolution on the surface. The addition of Na2SO4 effectively inhibited general corrosion of the steel because of a dense and continuous products layer enriched with more NaHSO4 and metallic sulphates formed.

Recovery of light and heavy rare earth elements from apatite ore using sulphuric acid leaching, solvent extraction and precipitation

Apatite is one of the important host minerals of the rare earth elements (REEs). Separation of REEs from apatite has not been studied extensively compared with other main minerals such as monazite, bastnasite and xenotime. Therefore, it is essential to develop an effective method for recovery of REEs from apatite-based ores.This paper presents the results of laboratory studies for the recovery of rare earth elements from an apatite ore sample by using sulphuric acid leaching, solvent extraction, and precipitation processes. Results showed that the most effective dissolutions of light REEs (>85%) and heavy REEs (>89%) from the apatite ore sample were achieved with a dilute sulphuric acid solution (1 M H2SO4) at a temperature of 20 °C in an hour. The heavy REEs present in the pregnant leach solution were almost entirely extracted using 1.2 M di-(2-ethylhexyl) phosphoric acid (D2EHPA) as a cation exchanger, while the most light REEs remained in the raffinate. The heavy REEs loaded into the organic phase were stripped completely by 3 M H2SO4 solution. REEs remained in raffinate and stripped into the aqueous solution were precipitated as RE oxalates by the addition of 0.08 M oxalic acid.

Evaluation of the synergistic properties of 4-hydroxy-3-methoxybenzaldehyde and 1, 4-diaminobenzene on the electrochemical corrosion behaviour of mild steel in dilute acid solutions

The electrochemical corrosion behaviour of the synergistic effect of 4-hydroxy-3-methoxybenzaldehyde and 1, 4-diaminobenzene on mild steel in dilute sulphuric and hydrochloric acid solution (1M concentration) with 1.5% recrystallized sodium chloride evaluated with weight loss analysis, potentiodynamic polarization test and optical microscopy. Statistical analysis of the results was done with Two-way ANOVA to assess their statistical significance of the experimental variables on inhibition efficiency values. Results show the combined organic derivatives performed effectively in both acids with average inhibition efficiency values above 85%. Observations from optical microscopy images further confirm the results of experimental data. Statistical derivations reveal the overwhelming significance of exposure time only inhibition efficiency values in both acids.

Inhibition Effect of N, N'-Dimethylaminoethanol on the Pitting Corrosion Austenitic Stainless Steel Type 304

The electrochemical influence and corrosion inhibition of N, N'-dimethylaminoethanol on the pitting corrosion resistance of austenitic stainless steel (type 304) in dilute sulphuric acid solution with sodium chloride addition was investigated using potentiodynamic polarization technique. Corrosion potential, pitting potential, repassivation potential, nucleation resistance, passivation range and repassivation capacity measurements and potentiodynamic analysis were used to evaluate the steel’s pitting resistance characteristics. The potentiodynamic experiments revealed that pitting potential increased with increase in concentration of the inhibiting compound coupled with an increase in the passivation range hence increased resistance to pitting g corrosion . DOI: http://dx.doi.org/10.5755/j01.ms.21.4.8977

Pitting corrosion inhibition of type 304 austenitic stainless steel by 2-amino-5-ethyl-1,3,4-thiadiazole in dilute sulphuric acid

The electrochemical behaviour and inhibitor protection of 2-amino-5-ethyl-1,3,4-thiadiazole (TTD) on the pitting corrosion of austenitic stainless steel (type 304) in dilute sulphuric acid solution contaminated with recrystallised sodium chloride was evaluated with the aid of potentiodynamic polarization method. TTD greatly reduced the corrosion rate of the steel with a corrosion inhibition efficiency ranging from 88.99–87.36%. The corrosion potential, pitting potential, repassivation potential, nucleation resistance, passivation range and repassivation capacity measurements and potentiodynamic studies were applied to assess the steel’s pitting resistance characteristics and behaviour in the acid chloride media. Results showed that pitting potential values increased with addition of TTD compound in conjunction with increase in the passivation range which strongly indicating increased electrochemical resistance to pitting corrosion.

Synergistic solvent extraction of manganese(II) with a mixture of Cyanex 272 and Cyanex 301 from chloride solutions

The solvent extraction of manganese(II) has been studied from chloride solutions using a mixture of Cyanex 272 and Cyanex 301 dissolved in kerosene. The mixture has shown a significant synergistic effect at XCyanex 272=0.6. The synergistic enhancement factor was calculated to be 14. The extracted species in the organic phase was found to be MnH2A2B2 using slope analysis method. Stripping experiments showed that manganese could be recovered using dilute sulphuric acid solutions from the loaded mixture. The mixture has a potential for the separation of Mn(II) from other associated metals.

Recovery Gemanium from Pulverized Fuel Ash through the Method of H<sub>2</sub>SO<sub>4</sub>-NH<sub>4</sub>F-NaClO<sub>3</sub> - Leaching-Tannin Precipitation

This paper will conduct a systematic study on method of recovering Ge from pulverized fuel ash in Lincang prefecture, Yunnan province. Details are like this, in view of the fact that Ge contained in pulverized fuel ash is wrapped up by a lot of Silica, Cao, magnesium oxide and is difficult to react with hydrochloric acid, so, first, have the pulverized fuel ash grinded to 200 meshes; then, ammonium fluoride should be put into 85-90°Cdilute sulphuric acid solution to produce hydrogen fluoride so as to destroy silicon dioxide and calcium oxide contained in the pulverized fuel ash. Meanwhile, dilute sulphuric acid solution dissolves magnesium oxide, by doing so, Ge will be released to react with sulfuric acid and produce Sulfuric acid Ge, and Ge will go into the solution；as for low state Ge（e.g,GeO,GeS）contained in the pulverized fuel ash which is difficult to be dissolved by sulfuric acid, sodium chlorate will be used as a kind of oxidant to change bivalence Ge into tetravalence Ge, then dissolve it into the solution, after the liquid-solid separation, sulfuric acid leaching solution rich in Ge will be obtained. Then, tannic acid will be used as precipitant to recover Ge from the leaching solution, and Ge concentrate will be produced through distillation and roasting. After this, put Ge concentrate on hydrochloric acid distillation to get germanium tetrachloride, After going through strenuous evaporation, distillation and hydrolysis, germanium dioxide with high purity will be yield. This paper has conducted conditional tests and discussion on the process parameters which will influence recovery Ge from pulverized fuel ash, including the dosage of Sulfuric acid, ammonium fluoride, sodium chlorate ,tannic acid and extraction time to find out the prior controlling condition of Ge recovery，under this prior condition, Ge leaching rate is as high as 84%，and tannic sinking Ge rate is as high as 98%. The pulverized fuel ash, after recovering Ge, can be used to backfill the mine pit, besides, most of the lixivium after recovering Ge can be recycled, and the rest of it will be released after neutralized up to the standard by lime. This process enjoys the following quality: high Ge recovery rate, less time used during the process ,less consumption of auxiliary material, easier to control the process, avoiding the potential pollution on the environment and lower cost involved in it, therefore, which is a kind of efficient and economic process of recovering Ge from pulverized fuel ash.

Thermodynamic model for acidic Fe(II) sulphate from solubility data

Acidic ferrous sulphate solutions are generated in a large scale in the hydro- and pyrometallurgical industries. They are also produced in the steel industry and titanium dioxide production. Acid mine drainage has long been a significant environmental problem in the coal and metal sulphide mining. The demand of recycling and reuse of materials has increased significantly especially in EU. Dumping and land filling a neutralised deposit is not an option anymore. Thus, efficient techniques of recycling and reuse of sulphuric acid and/or metal sulphates from the side streams are needed.When developing alternative solutions, a better understanding of the thermodynamic behaviour of the FeSO4–H2SO4–H2O system is needed. In the present study a thermodynamic model of this system has been developed, in order to yield a thermodynamically consistent set of values for the solubility of iron sulphate in a wide temperature and concentration range. The current model presents the experimental data available with a good accuracy and consistently up to 100°C, and sulphuric acid concentrations up to 10mol/kg. The model also predicts well the solubility measurements available in dilute sulphuric acid solutions at 160–220°C.

Modelling of ion-exclusion chromatography and vacancy ion-exclusion chromatography of selected aromatic acids on strongly acidic resin in the H+form

Summary Ion-exclusion chromatography (IEC), a chromatographic technique based on exclusion of dissociated sample molecules, finds many applications in a variety of analytical separations of weak acids. Vacancy ion-exclusion chromatography (v-IEC) is an alternative technique in which the column is equilibrated with the sample solution flowing as mobile phase through the system, and pure water is injected as the sample. In this technique, characteristic negative ‘vacant’ peaks are obtained. The objective of the work described in this paper was to describe the mechanisms of retention in IEC and v-IEC for selected aromatic acids, under analytical and concentration-overload conditions, with pure water, dilute sulphuric acid solution, and dilute sulphuric acid containing a small amount of heptanol as the three mobile phases. The retention times and peak shapes predicted by use of the model were in good mutual agreement for a wide range of concentrations for all the analytes investigated.

Acidic degradation and enhanced antioxidant activities of exopolysaccharides from Cordyceps sinensis mycelial culture

abstract An exopolysaccharide (EPS) fraction isolated from mycelial culture of a Cordyceps sinensis fungus, desig-nated EPS-1 with an average molecular weight (MW) of 38 kDa, was hydrolysed in dilute sulphuric acidsolution at pH 1 and 90 C, yielding two major MW fractions, 3.0 kDa and 30 kDa, respectively. While theproportion of lower MW fraction increased with the hydrolysis period (18% in 0.5 h and 92% in 10 h), thepolydispersity (M w /M n ) of EPS decreased steadily (from 1.47 initially to 1.10 in 10 h). The IR spectra ofhydrolysed EPS fractions showed changes only in the C–O–C and C–O–H band peaks from that of EPS-1. These results suggest that the hydrolysis of EPS in the acidic solution caused the EPS degradationmainly by cleaving the glycosidic linkage but no change in the primary molecular structure. The hydro-lysed EPS fractions had much higher (30–80%) antioxidant and radical-scavenging activities. 2009 Elsevier Ltd. All rights reserved. 1. IntroductionCordyceps sinensis (Berk.) Sacc., generally called Cordyceps orDong-Chong-Xia-Cao (winter worm–summer grass) in Chinese, isa precious and famous medicinal fungus in China which has beenused as a general tonic and therapeutic herb by the Chinese overhundredsof years.Cordycepshasshown a broadrangeof health ef-fects on the immune, kidney, liver and cardiovascular functions,and antitumor and antioxidation activities (Li & Tsim, 2004;Russell & Paterson, 2008; Zhu, Halpern, & Jones, 1998). NaturalCordyceps is a rare and endangered species insufficient to meetthe demand, and mycelial fermentation is a more economicaland sustainable process for production of Cordyceps mycelial bio-mass and polysaccharides. Polysaccharides represent a major classof bioactive compounds in Cordyceps and many other medicinalmushrooms which have anticancer and immunomodulation activ-ities, and other notable health effects such as antioxidation andhypoglycemic activity (Li & Tsim, 2004).Since oxidative stress evoked by reactive oxygen species (ROS)is harmful to human health and a potential cause of many humandiseases (Halliwell & Gutteridge, 1998), the antioxidant propertiesof functional foods and herbal products are important for healthprotection and disease prevention. Numerous previous studieshave examined the antioxidant and radical-scavenging activitiesof water extracts of natural Cordyceps and cultivated fungal myce-lia (Dong & Yao, 2008; Li, Dong, & Tsim, 2001; Yamaguchi, Kagota,Nakamura, Shinozuka, & Kunitomo, 2000). As the major constitu-ents of water extracts, polysaccharides are attributable to theirantioxidant activities. A few studies have also shown the antioxi-dant activities of purified polysaccharide fractions isolated fromCordyceps species, such as the one isolated from C. sinnesis myceliaprotecting against hydrogen peroxide-induced damage of PC12cells in culture (Li et al., 2003), and the one from cultivated C. mil-itaris fruit bodies scavenging hydroxyl radicals (Yu et al., 2007).The application and efficacy of polysaccharides for health care isdependent not only on the chemical structure but also on themolecular size or molecular weight (MW), which has a direct influ-ence on solubility and viscosity in solution, and usually also on thebioactivity (Shahidi, Arachchi, & Jeon, 1999). Most of the polysac-charides isolated from various Cordyceps species are of high aver-age MW over 10 kDa, usually from 50 to 1000 kDa (Leung, Zhao,Ho, & Wu, 2009). Moderate degradation of the high-MW polysac-charides may increase the water solubility and decrease the viscos-ity in solution, thus improving the medicinal properties. Moderatedegradation has also been shown to improve the antioxidant activ-ities of natural and modified polysaccharides, such as ulvan (fromseaweeds, Chorophyta) (Qi, Zhao, Zhang, & Zhao, 2005) and chito-sans (Xing, Liu, Guo, & Yu, 2005). While the polymer degradationcan usually be accomplished through chemical, enzymatic and

Enhanced leachability of gold and silver in cyanide media: Effect of alkaline pre-treatment of jarosite minerals

Composite samples of tailings containing gold (1.35 g/t) and significant amounts of silver (155 g/t) were subjected to batchwise cyanide leaching to assess the feasibility of extracting gold and silver. The tailings are waste solids arising from flotation and leaching operations whereby the flotation product (sphalerite concentrate) is calcined and then solubilised into dilute sulphuric acid solution and eventually sequestered from the electrolyte by electrowinning. Silver and gold are part of the zinc refinery residue, flotation tailings and to a limited extent the calcine leach tailings. Mineralogical results showed that composite tailings are refractory in nature (44% quartz, 17% silico aluminates and 12% jarosites). The concept of enhancing gold and silver recovery from the tailings focused on firstly decomposing the jarosite minerals by alkaline pre-treatment and then secondly leaching with cyanide solution. These two steps ensured that free gold and silver found in the zinc refinery residue and in the jarosite minerals could be leached simultaneously. The composite tailings were treated with Ca(OH) 2 solutions and then heated to 90 °C for 2 h to decompose the silver-bearing mineral (Ag,PbFe 3(SO 4) 2(OH) 6). The alkaline pre-treated tailings were then subjected to cyanide leach tests at different NaCN dosages (2.5–10 kg/t) and particle size (96–200 μm). Without an alkaline pre-treatment stage, leach efficiencies achieved were 41% and 25% for gold and silver, respectively at 40 °C and 8 h mixing time. But, better leach efficiencies (55% for Au, 81% for Ag) were achieved after the feed was pre-treated with Ca(OH) 2. The leaching mechanism of gold was explained by the shrinking sphere model denoted by surface chemical reaction.

Integrated bacterial process for the treatment of a spent nickel catalyst

Integrated biological processes involving the dissolution and subsequent precipitation have been used for the treatment of the spent material from the hydrogenation of vegetable oil containing a high-level of nickel. Our results show that nickel was successfully leached using Acidithiobacillus thiooxidans. The percentages of nickel leached using A. thiooxidans were higher than those obtained with dilute sulphuric acid solutions. Due to the physical characteristics of the residue, the best results were obtained when the leaching process was carried out using sulphuric acid biogenerated by an A. thiooxidans biofilm. The recovery of nickel from the leachates was performed at room temperature by precipitating with sulphide generated by Desulfovibrio cells. Indirect precipitation using sulphide generated in Desulfovibrio sp . cultures allowed the recovery of nickel as the very insoluble nickel sulphide.

Dissolution of mechanically activated Panzhihua ilmenites in dilute solutions of sulphuric acid

Dissolution of mechanically activated Panzhihua ilmenite was conducted in 5–20% sulphuric acid solutions. With high milling intensity the milling atmosphere significantly affected the dissolution with milling under vacuum almost double the dissolution of ilmenite milled in air. This was due to formation of a lot of acid-resistant pseudorutile and lowering level of the lattice strains, especially in the c-axis direction of the ilmenite unit cell, upon milling in air. Under the experimental conditions applied, titanium and iron dissolved at a nearly stoichiometric ratio. Hydrolysis of the dissolved titanium, however, was also in progress simultaneously. The sulphuric acid concentration and reaction temperature remarkably influenced the hydrolysis rate, thus affecting the microstructure of the hydrolysate. In 5 wt.% and 10 wt.% acid solutions, the hydrolyzed product was poorly compacted and dissolution could continue. In contrast, the product in 20 wt.% acid exhibited a compact structure and was strongly adherent preventing further dissolution of the un-reacted ilmenite. In both cases the hydrolysis product appeared to be rutile TiO 2. The experimental results showed that significant hydrolysis was inevitable when the acid concentration was ≤ 20 wt.%. Therefore, preparation of synthetic rutile from mechanically activated ilmenite is a better alternative to direct production of pigment TiO 2. And the method could directly and fully reuse the spent acid discharged in the sulphate process.

Heat Exchanger Fouling and Cleaning in the Dihydrate Process for the Production of Phosphoric Acid

Crystallization fouling and cleaning mechanisms of calcium sulphate from phosphoric acid solution have been studied experimentally and theoretically during forced convective heat transfer. The effects of flow velocity, foulant concentration, surface and bulk temperatures on the formation of scale and its removal are investigated. Close examination of the heat transfer surface at the end of a cleaning period with a cleaning agent containing 5 wt% sulphuric acid reveals that significant deposits still remained on the surface. The remaining deposits were rippled, hard and difficult to remove chemically. After clarification of the effects of operating parameters on the deposition and cleaning processes, the results of the experiments are used to develop mechanistic models for the prediction of fouling resistances of calcium sulphate during forced convective heat transfer, and for removal of the deposits by dilute sulphuric acid solutions. The predictions of the suggested models for fouling and cleaning are compared with measured data. Deviations ranging from 7% to 12% are observed which confirm the suitability of the models.

Effect of thiourea on sulphuric acid leaching of bastnaesite

The possibility of leaching bastnaesite pre-concentrate in dilute sulphuric acid solutions at 25 °C was studied. For this purpose, unroasted and roasted bastnaesite pre-concentrates were leached with 100 mL of 1–3 M H 2SO 4 and H 2SO 4+thiourea solutions at 25 °C with a liquid/solid ratio of 20 mL/g for 6 h. Roasting affected the dissolution behaviour of rare earths in H 2SO 4 solution and dissolution of total rare-earth elements (REEs) was increased from 8.5% to 47.4%. The addition of thiourea to the leaching medium further increased the dissolution of the rare-earth elements in the unroasted and especially in the roasted pre-concentrate due to the reduction of cerium (IV) to cerium (III) by thiourea, thus increasing the cerium dissolution value from 22.8% to 93.0%, which in turn increased the total dissolution of REEs from 17.6% to 89.0%. Thus, it was possible to precipitate 93.6% (CeO 2=92.4%, La 2O 3=93.2%, Nd 2O 3=98.4%) of total REEs in the filtrate and the total REO content of the precipitate was determined as 92.6% (CeO 2=58%, La 2O 3=29%, Nd 2O 3=5.6%).