Claims:WE CLAIM

1. A method for preparing a magnesium salt and micro silica from peridotite rock, wherein the method comprising:
crushing the peridotite rock, wherein the peridotite rock is crushed with pulverizing to a size of -150 microns;
leaching the crushed peridotite rock, wherein the crushed peridotite rock is leached in oxidative agent by varying acid concentration, leaching temperature and leaching time, and stirring speed;
obtaining a leach slurry, wherein the leach slurry is filtered to separate magnesium leach liquor and the undissolved residue;
purifying the magnesium leach liquor to obtain purified magnesium leach liquor, wherein the magnesium leach liquor is purified by adjusting the pH of 7-8 using sodium hydroxide to remove iron and impurities;
dehydration of the purified leach liquor to form magnesium sulphate salt;
precipitating the magnesium hydroxide salt, wherein magnesium hydroxide salt is precipitated by adjusting pH to 11-12 to precipitate magnesium as hydroxide which on separation through filtration to obtain magnesium hydroxide salt.

2. The method of claim 1, wherein the oxidative leaching converts peridotite rock to magnesium rich leach liquor and a siliceous residue with silica size in 10-30 microns range without hindering the filtration step.

3. The method of claim 1, wherein the oxidative leaching is carried in a flat bottom flask placed on a hot plate comprising of magnetic stirring with temperature sensor for continuous monitoring and maintenance of the set temperature

4. The method of claim 1, wherein the silica acid formation is controlled by addition of an oxidative agent such as dilute H2SO4 thereby converting the dissolved silica into quartz.

5. The method of claim 1, wherein the oxidative agent be subjectively added at start of oxidative leaching or continuously during oxidative leaching or at regular interval during oxidative leaching or at end of oxidative leaching.

6. The method of claim 1, wherein the oxidative agent controls the formation of the silicic acid formation thereby hinder the formation of gelatinous residue.

7. The method of claim 1, wherein magnesium leach liquor is purified to remove impurities such as hydroxides.
8. The method of claim 1, wherein the purified magnesium leach liquor can be converted to either the magnesium sulphate salt or the magnesium hydroxide salt based on the requirement.

9. The method of claim 1, wherein the residue obtained after oxidative leaching contains micro silica in micron size range.

10. The method of claim 1, wherein the magnesium extraction efficiency is ~92%.

, Description:PRIORITY INFORMATION
[001] The patent application doesn’t claim priority form any patent application.

FIELD OF THE INVENTION
[002] The present subject matter described herein generally relates to method for preparing Magnesium salt and Micro silica and more specifically to a process of converting peridotite rocks of chromite ore overburden into Magnesium salt and Micro silica as an alternative source of Magnesium.

BACKGROUND
[003] Magnesium has two important mineral classes such as carbonates and silicates. Carbonate minerals of magnesium include dolomite and magnesite whereas, Olivine, Pyroxenite etc., are some of the Magnesium silicate minerals. Despite of the relatively high Magnesium content in the silicate minerals, carbonates are used industrially to produce various Magnesium based derivatives due to the easiness in their processing. Apart from the high Magnesium content, magnesium silicate minerals like forsterite have high melting point hence, could be suitable for high temperature applications like refractories. Most of the times Magnesium silicates co-exist with iron silicate to form a solid solution in olivine. Presence of iron silicate renders usage of olivine as a refractory material unusable as it forms a low melting phase. Many attempts have been made to use olivine and peridotite (olivine and pyroxenite mixture) etc., as a refractory material.

[004] Conventionally, calcination of carbonate sources of Magnesium like magnesite and dolomite is used to produce MgO which in turn generates huge amount of CO2. Every tonne of magnesite releases nearly half tonne of CO2. Hence, it is essential to replace conventional carbonates with silicates to address environmental issues associated with usage of carbonates.

[005] Mining activity around the world has increased significantly during 20th century to meet the increased demand for various metals. This has resulted in generation of enormous amount of overburden and other waste materials along with the valuable mineral matter Mining of low grade ores further increases the amount of overburden/waste per ton metal equivalent of ore mined. In this respect, increasing the recycling and re-use potential of overburden/low grade ores may provide sustainable and cost-effective alternatives to overcome the challenges associated with their disposal and management. Currently, the most common use of overburden and other mine waste is in construction industry and as feedstock for making cement and concrete. But the overburden can also be used as a source to generate valuable minerals and metals.

[006] Hydrometallurgy is proven to be a successful process for the treatment of low-grade ores and mine waste that cannot be treated economically through the high temperature route. During mining of Sukinda chromite ores of India, magnesium silicate rocks like olivine, pyroxenite, dunite and peridotite etc., forms major part of the overburden. Currently they do not find any usage and hence are not being utilized. But magnesium silicates like olivine and serpentine are attractive sources for magnesium (Mg) and contains relatively high Mg content. Also, they are attractive and environment friendly alternative to the conventional carbonate sources. Carbonate source of Mg has negative effect on the global carbon balance. So, the usage of magnesium silicate as a source of Mg will address the challenges associated with their storage and handling, and also the CO2 gas that gets released during processing of conventional carbonate sources.

Prior Arts

[007] EP1373139B1 describes a method for the manufacture of silica (SiO2) and various magnesium compounds from olivine mineral ((Fe, Mg)2SiO4). Olivine is mixed with concentrated H2SO4 at olivine/sulphuric acid in the range of 1 to 0.3 and the mixture is heated between 150° C – 400° C for 3-12 hours. Thereafter the mixture is leached in water to produce a filtrate containing dissolved Mg and an undissolved silica. The filtrate and silica were separated though filtration. The filtrate solution is further processed to produce magnesium sulphate salts. Silica filter product is further washed using weak solution of soda or sodium hydroxide and thereafter with a weak solution of an acid or a mixture of acids to obtain a pure silica product.

[008] WO2002048036A1 describes a method for the extraction of silica and magnesium compounds, by chemical and thermal treatment of olivine. The method comprises sulphasting of olivine at an olivine/sulphuric acid weight ratio of ~ (0.5-0.67) and heating the mixture at 250°C for ~ 8 hours. Sulphasted mixture was thereafter dissolved in water, whereby silica precipitates to a solid which after its filtration is purified in a weak solution of soda, and eventually with a weak aqueous solution of an acid or a mixture of acids. This method provides manufacturing of a purified silica solid, leaving a filtrate consisting mainly of dissolved magnesium which after further processing is transformed to magnesium compounds.

[009] CN108439440 describes a technology to produce MgO from peridotite ore through acid leaching using H2SO4 at 80-90o C. In the method high purity oxygen is used to take out Fe impurity. The magnesium hydroxide obtained was dried and calcined. It was then dissolved with HCl. A mixture of high purity carbon dioxide and sent into the above mixture. Basic magnesium carbonate is obtained on solid liquid separation which was dried and calcined to give MgO.

[0010] CN108658103 relates to a method of producing magnesium oxide using peridotite ore and it involves soaking the ore in acid, separating the residue and pickling solution, removal of Ni from the pickling solution, settling the magnesium ions in the solution as hydroxide, and calcining the same to produce MgO. The production efficiency of the process is good and also is the product quality. It has decreased pollution because of the utilization of by-products.

[0011] CN108658104 puts forward a technology to produce MgO from peridotite mine. The technology comprises grinding, acid leaching, purification through floatation and magnesium precipitation. Magnesium extraction rate and the purity are cooperatively accelerated through proper grinding. The purity of prepared magnesium can be 99.7%or above, the magnesium oxide extraction rate can be 89.7-94.2%.
[0012] US5091161 describes a method to continuously produce pure MgCl2 solution from the siliceous magnesium minerals using HCl and at temperatures higher than 50o C and less than boiling point. Reactive magnesia was used as a means of pH neutralizing for bulk impurity removal. It also prevents silica gel formation and thus eliminates the need to boil the slurry solution.

[0013] US2549798 has shown that separation of silica and leach liquor after the leaching can be accomplished rapidly by incremental addition of one reactant to other. Thereby the formation of silica gel and silicic acid during the hydrometallurgical treatment of magnesium silicates was inhibited substantially. This approach has also minimized the amount of Mg that gets entrapped in the residue during filtration.

[0014] Thus, most of the literature available on magnesium silicates is either on olivine and serpentine. Some of the processes uses a pre-treatment operation like thermo-chemical treatment and grinding of ore before leaching to improve the dissolution kinetics as in case of leaching serpentine. Also, some literature highlights the use of high temperature and low pressure for controlling the silica gel formation issue from the dissolved silica. Other approaches refer to controlling the silica gel formation including addition of reactive magnesia, calcined serpentine and step wise addition of one reactant to other etc. But, such method are not economic or 100% effective.

OBJECTIVE OF THE INVENTION

[0013] An object of the present subject matter is to provide process of converting Peridotite rocks of chromite ore overburden into Magnesium salts and Micro silica as an alternative source of Magnesium.
[0014] Another object of the present subject matter is to provide a method for preparing magnesium salts and micro silica using the alternative Mg resources.
[0015] Another object of the present subject matter is to utilize the oxidative leaching method by addition of oxidation agent such as hydrogen peroxide for controlling the most common silica gel formation issue that persists during aqueous processing of silicate minerals.
[0016] Yet another object of the present subject matter is to provide a process for complete conversion of peridotite rock into two valuable products i.e, Mg salts such as MgSO4 and Mg(OH)2 and, a micro silica residue using H2SO4 as lixiviant agent at atmospheric pressures and temperatures less than 100o C.

SUMMARY OF INVENTION

[0017] Before the present system is described, it is to be understood that this application is not limited to the particular method or process, as there can be multiple possible steps/embodiments that are not expressly illustrated in the present disclosures. It is also to be understood that the terminology used in the description is for the purpose of describing the particular process only and is not intended to limit the scope of the present application. This summary is provided to introduce aspects related to a process of converting peridotite rocks of chromite ore overburden into Magnesium salt and Micro silica as an alternative source of Magnesium, and the aspects are further elaborated below in the detailed description. This summary is not intended to identify essential features of the proposed subject matter nor is it intended for use in determining or limiting the scope of the proposed subject matter.
[0018] The present subject matter describes a method for preparing a magnesium salt and micro silica from peridotite rock. The method comprises crushing the peridotite rock, wherein the peridotite rock is crushed manually followed by pulverizing to a size of -150 microns. Further, leaching the crushed peridotite rock, wherein the crushed peridotite rock is leached in dilute H2SO4 by varying acid concentration, leaching temperature and leaching time, and stirring speed, wherein an oxidative agent such H2O2 is used to control formation of gelatinous residue. Furthermore, obtaining a leach slurry, wherein the leach slurry is filtered to separate magnesium leach liquor and the undissolved residue. Purifying the magnesium leach liquor to obtain purified magnesium leach liquor, wherein the magnesium leach liquor is purified by adjusting the pH of 7-8 using sodium hydroxide to remove iron and impurities. Dehydration of the purified leach liquor to form magnesium sulphate salt. Precipitating the magnesium sulphate salt, wherein magnesium sulphate salt is precipitated by adjusting pH of 11-12 to precipitate magnesium as hydroxide which on separation through filtration to obtain magnesium hydroxide salt. Further, the residue obtained after oxidative leaching contains micro silica in micron size range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The foregoing summary, as well as the following detailed description of embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, there is shown in the present document example constructions of the disclosure, however, the disclosure is not limited to the specific methods and device disclosed in the document and the drawings. The detailed description is described with reference to the following accompanying figures.

[0019] Figure 1 illustrates an Eh-pH diagram for Mg-Si-H2O system using Factsage 7.2, in accordance with an embodiment of the present subject matter.

[0020] Figure 2 illustrates a XRD of peridotite rock, in accordance with an embodiment of the present subject matter.

[0021] Figure 3(A) illustrates a SEM-Mapping image of peridotite rock, in accordance with an embodiment of the present subject matter.

[0022] Figure 3(B) illustrates a Point EDS of peridotite rock, in accordance with an embodiment of the present subject matter.

[0023] Figure 4 illustrates diagram of a system set-up for leaching, in accordance with an embodiment of the present subject matter.

[0024] Figure 5 illustrates SEM-Mapping image of a residue particle showing two regions, a Mg rich and a silica rich portions, in accordance with an embodiment of the present subject matter.

[0025] Figure 6 illustrates silica residue obtained after oxidative leaching by addition of H2O2 (a) before starting of experiments (b) at the end of experiment, in accordance with an embodiment of the present subject matter.

[0026] Figure 7(A) illustrates Magnesium sulphate salt produced by dehydrating the Mg leach liquor, in accordance with an embodiment of the present subject matter.

[0027] Figure 7(B) illustrates Magnesium hydroxide salt produced by pH adjustment to 12, in accordance with an embodiment of the present subject matter.

[0028] The figure depicts various embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

[0029] Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words "comprising", “having”, and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any process and methods similar or equivalent to those described herein can be used in the practice, the exemplary method for preparing magnesium salts and micro silica is now described. The disclosed process is merely example of the disclosure, which may be embodied in various forms.
[0030] Various modifications to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art will readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated but is to be accorded the widest scope consistent with the principles and features described herein.

[0031] The present subject matter describes peridotite rock as a source for obtaining magnesium salt and micro silica. The complete utilization of olivine has been reported which utilizes high temperature sulphasting. In this respect, magnesium silicates is an attractive alternative source. Apart from the relatively high magnesium content, silicate minerals of magnesium like olivine, serpentine etc. have high acid solubility. The extraction of magnesium from its silicates using lixiviant agents such as H2SO4 and HCl etc. is known. However, the extraction process using hydro-metallurgical processing of silicate minerals leads to formation of silicic acid formation which further leads to gelation of residue which significantly hinders the filtration step after leaching which in turn thus affects the productivity.

[0032] The Figure 1 illustrates an Eh-Ph diagram for Mg-Si-H2O system using Factsage 7.2. The water stability region indicates that at pH<5, Mg+2 and H4SiO4 are the stable species. H4SiO4, also known as silicic acid is resultant of the dissolved silica (H4SiO44-) reaction with H+ ions in acidic solutions as per reaction 1. Silicic acid on polymerization leads to formation of poly silicic acid as per reaction-2. This poly silicic acid particles grows to further branch and cross-link leading to formation of silica gel. This silica gel entraps the undissolved solid particles of residue and thus hinders the solid liquid separation. So, for the seamless conversion of peridotite into Mg rich liquor and siliceous residue, it is very much essential to control the gelation of residue.

[0033] In one implementation, the present description the process of converting peridotite rocks of chromite ore overburden into Magnesium salts and Micro silica. A peridotite rock as received originally is very hard and lumpy. To perform the process the peridotite rock is initially manually crushed followed by pulverizing to a size of -150 microns. The crushed peridotite rocks are characterized using different characterization techniques like XRD (X-Ray Diffractogram), chemical analysis, and SEM etc. Based on the XRD characterization conducted peridotite rock is found to contain 40.52% MgO, 34.38% SiO2 and 6.15% Fe (Total) by weight. Detailed chemical composition of peridotite rock is as given in Table 1.

Element/ Compound Fe(T) CaO SiO2 S MgO MnO Al2O3 Cr2O3 LOI P
Wt.% 6.15 0.22 34.38 0.013 40.52 0.03 0.38 1.26 13.84 0.04
Table. 1

[0034] Further, based on the XRD characterization it is observed that the major mineral phase of the peridotite rock is olivine (a solid solution between forsterite and fayalite) with minor amount of Lizardite. Lizardite is a hydrated magnesium silicate rock which is formed due to natural weathering of magnesium silicates. The Figure 2 illustrates the XRD of the peridotite rock.

[0035] The Figure 3(A) illustrates the SEM (scanning electron microscope) mapping of peridotite rock. The mapping contains very small particles of chromite and iron oxide with size of~100 µm. The particles are present in the magnesium silicate matrix surrounding them. Phases corresponding to iron oxide and chromite were not detected in XRD as their weight fraction is very small in the rock hence falls below the detection limit of XRD. Further, the Figure 3(B) illustrates the EDS (Energy-dispersive detector) of peridotite rock obtained at different locations on the rock and Table 2 illustrates their point EDS analysis data.

Point/ wt% O Fe Mg Si Cr Al
1 22.9 75.3 1.2 0.5 - -
2 22.2 77.7 - - - -
3 22.9 75.1 1.4 0.5 - -
4 31.5 18.9 4.1 - 39.7 5.7
5 35.9 37.2 4.4 22.4 - -
6 31.4 19.1 4.0 - 39 6.1
7 31.4 22.0 3.9 - 37.6 5.4
8 31.6 19.6 5.0 - 37.8 5.8
9 45.2 4.4 27.8 22.5 - -
10 46.2 2.0 27.4 24.2 - -
Table. 2

[0036] Referring now to Figure 4, the Figure illustrates the set-up of a system for conducting a leaching experiment. The setup includes a flat bottom three neck flask and, a hot plate with provisions for stirring the leach slurry magnetically and with temperature sensor for continuous monitoring and maintenance of the set temperature. In one embodiment, leaching experiments are carried out in dilute H2SO4 by varying acid concentration, leaching temperature and leaching time, and stirring speed. The leaching experiment is carried out by varying leaching time, temperature, stirring speed and acid concentration.

[0037] In one embodiment of the subject matter, the leaching method is carried out at atmospheric pressure and temperatures less than 100o C. Further, the peridotite rock characterized using XRD, SEM and Chemical analysis identifies the phases present, their distribution in the rock and its chemical composition respectively. The characterized pulverized peridotite rock powder is leached leaching in dilute H2SO4 by varying acid concentration, leaching temperature and leaching time, and stirring speed. The obtained leached slurry is filtered to separate magnesium leach liquor and the undissolved residue. The obtained leach liquor is purified by adjusting the pH to ~8 using sodium hydroxide to remove Fe and other impurities as hydroxides. In further steps, the purified leach liquor is dehydrated to form magnesium sulphate salt. The pH is further adjusted to 12 to precipitate magnesium as hydroxide which on separation through filtration leads to magnesium hydroxide salt.

[0038] In one embodiment, the oxidative leaching to convert the dissolved silica into quartz controls the silica gel formation observed during the normal leaching using H2SO4 alone. In another embodiment, different concentrations of oxidizing agent and the approaches for their addition to the leach slurry are used to determine their effect on controlling silica gel formation and efficiency of magnesium extraction.

[0039] In one implementation, it is noted that only leaching temperature and acid concentration have significant effect on the magnesium extraction efficiency. In one exemplary condition temperature of 900C and concentration of 1M the highest magnesium extraction efficiency of ~ 72% was achieved. This efficiency is less due to low acid concentration and formation of silicic acid that forms on dissolved silica reaction with H+. The silicic acid formed either gets precipitated on the particle surface or else polymerizes to polysilicic acid thereby leading to gelation.

[0040] Further, SEM image of the residue obtained after leaching is as illustrated in Figure 5. The Figure 5 illustrates SEM image of a residue particle showing two regions namely a Mg rich portion and a silica rich portion on an undissolved peridotite particle. The silica rich layer may be broken by means of increasing the leaching temperature and/or acid concentration which further improves the dissolution of magnesium.

[0041] In another embodiment, experiments are conducted only by increasing the leaching temperature and acid concertation to increase the dissolution of magnesium. Table 3 shows the extraction of magnesium at different acid concentrations and leaching temperatures.
H2SO4 concentration Mg leaching efficiency
RT 50 C 70 C 90 C
0.5M 32.95 45.16 46.98 45.97
1M 42.04 66.68 61.76 72.13
1.5M 59.17 71.13 89.27 90.99
2M 64.11 77.26 94.55 94.90
2.5M 85.87 87.60 94.70 94.25
Table 3

[0042] In one exemplary condition maximum magnesium extraction efficiency of ~94% was achieved at concentrations of 2M, temperature of 700C, 400 RPM and pulp density of 10%. In this regard, oxidative leaching of the peridotite using H2O2 as oxidizing agent was carried out at the optimized leaching conditions derived from normal leaching experiments. A further increasing temperature and concentration does not any effect on the extraction efficiency of magnesium. Hence, the optimum conditions in an exemplary condition maybe 2M and 70oC. Furthermore, it was observed that the formation of silica gel hindered the filtration process.

[0043] In one exemplary condition, the silica gel and dissolved silica be converted into quartz by oxidation thereby resolving the formation of gelatinous residue.

[0044] In one exemplary condition, various methods of oxidizing agent addition and its concentrations are experimented. The concentration of H2O2 used in the current study is 0.5 and 1M. Different methods are employed for addition of oxidizing agent i.e. (a) at start of the leaching experiment (b) continuously during the leaching experiment (c) at regular interval during the leaching experiment; (d) at the end of the leaching experiment. Table 4 indicates the comparison of magnesium efficiency and the gel formation tendency under different concentration of H2O2 and using different approaches for its addition. It is noted that the in normal leaching conditions i.e. without any oxidizing agent, the dissolved silica hindered the filtration step (gravity filtration). For the initial few minutes filtration happened but later it completely stopped due to gelatinous nature of the residue. In case of oxidative leaching and using all the approaches the formation of gelation was resolved and the filtration happened seamlessly within 2 hours. Mg extraction efficiency noted was as high as ~92% and the leftover residue contained silica with size 10-30µm.

Mg Efficiency Gel formation
Normal leaching No H2O2¬ 94.55 Gel formed completely hindered filtration
Continuous
0.5M H2O2 92.46
Gelation controlled and filtration completed in < 2 hours
Regular 91.71
Starting 92.01
Ending 91.38
Continuous
1M H2O2 89.91
Regular 92.64
Starting 90.66
Ending 89.66
Table 4

[0045] Furthermore, the Figure 6 illustrates a SEM image of the residue obtained after oxidative leaching. Figure 6 illustrates silica residue obtained after oxidative leaching by addition of H2O2 (A) before starting of experiments (B) at the end of experiment. It is noted that the compared to the residue remaining after oxidative leaching by addition of H2O2 at the starting of experiment, the residue obtained by adding H2O2 at the end of the experiment has silica particles with less size. The reason for the difference is due to the fact that the silica particles formed when H2O2 is added at the starting which provides sufficient time and energy to grow and agglomerate.

[0046] In one embodiments, the leach liquor obtained after leaching are purified by adjusting the pH to ~8 using sodium hydroxide to remove iron and other impurities such as hydroxides. The purified leach liquor can be either dehydrated leading to magnesium sulphate salt as shown in Figure 7(A) or on further pH adjustment to ~12 can lead to magnesium precipitation as magnesium hydroxide as shown in Figure 7(B). Figure 7(A) illustrates Magnesium sulphate salt produced by dehydrating the Mg leach liquor. Figure 7(B) illustrates Magnesium hydroxide salt produced by pH adjustment to 12. Chemical analysis of Mg(SO)4.xH2O and Mg(OH)2.xH2O that are produced is shown in below Table 5 and Table 6 respectively indicating that the salt obtained are pure.

Wt% MgSO4 Cl Fe Al Si Pb
MgSO4 produced 39.19 0.020 0.006 0.014 0.047 0.004
Table 5

Wt% MgO Cl SO4 Fe Al Si Pb, ppm
Mg(OH)2 produced 43.82 0.273 0.132 0.036 0.120 0.008 <1
Table 6
[0047] Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include those provided by the following features.
[0048] Some embodiments enable use of oxidative leaching of peridotite rock to produce two valuable products i.e. magnesium salt and a micro silica residue
[0049] Some embodiments enable low cost and environment friendly method for preparing magnesium salt and mirco silica.
[0050] Some embodiments enable further processing to obtain magnesium sulphate salt and magnesium hydroxide salt from magnesium leach liquor.
[0051] Although embodiments of the process of converting peridotite rocks into Magnesium sulphate salt and Micro silica are explained, it is to be understood that the appended claims are not necessarily limited to the specific process described. Further, the specific p are disclosed as examples of embodiments of process of converting peridotite rocks into Magnesium leach liquor and Micro silica.