Descaling method for scale of nickel leaching autoclave in HPAL (High Performance Liquid ALL) process

Abstract

The invention discloses a descaling method for scale of a nickel leaching autoclave in an HPAL process. The method comprises the following steps: adding caustic soda liquid into a nickel leaching autoclave to be descaled, carrying out high-temperature descaling reaction in a stirring state, and removing residual caustic soda after the reaction is finished, so as to obtain the nickel leaching agent, the pH value of the high-temperature descaling reaction is 13.5 to 14. According to the method, by strictly controlling parameters such as liquid caustic soda concentration, temperature and time in the reaction process, after alkali-soluble components in a structure are dissolved by using liquid caustic soda, compact structures in scales are destroyed, so that the scales are loose and porous and fall off from the inner wall of the high-pressure kettle under the stirring action, and the scale in the high-pressure kettle is removed while ensuring that the scales in the high-pressure kettle are removed. A titanium layer on the inner wall of the autoclave is prevented from being corroded; the method is simple in process and convenient to operate, the technical problem that an existing descaling process excessively depends on manpower can be effectively solved without additionally adding equipment, according to tests, the descaling rate is 95% or above when the technical scheme is adopted for high-pressure kettle descaling, and the obtained alkaline residues can serve as a neutralizing agent for neutralizing HPAL process tailings to be recycled.

Description

Technical Field

[0001] The present invention relates to a method for removing scale from an autoclave, specifically to a method for removing scale from the scale formed in a nickel leaching autoclave in the HPAL process, and belongs to the field of hydrometallurgy. Background Art

[0002] High-Pressure Acid Leaching (HPAL) is a process used to extract nickel from laterite nickel ore. This process plays an important role in global nickel production. With the increasing demand for resources and the requirements of environmental protection, the role of the HPAL process has become more prominent. However, during the production process, the problem of scale formation in the autoclave has always been a difficult problem that the industry pays attention to and focuses on research. Scale formation in the autoclave not only affects the effective volume of the equipment, but also causes changes in the fluid model in the autoclave, increased wear of the stirring paddle blades, and an increase in the failure rates of the mixer seals and speed reducers.

[0003] The autoclave has 7 compartments, and each compartment has a single-layer stirring with 4 paddle blades. Pulp, steam, and concentrated sulfuric acid are introduced into the first compartment, and steam and concentrated sulfuric acid are introduced into the second compartment. Through production practice, scale formation mainly occurs in the liquid phase space inside the autoclave. The scale on the smooth inner wall of the autoclave is relatively uniform, and the scale is severe at the stirring, baffle plate, partition plate, corners, etc.; the inner wall of the gas phase space of the autoclave basically does not form scale, but the scale is severe at the stirring and the connecting flange at the upper end of its shaft. The typical scale surfaces in the first and second compartments are flat and dense, showing a dark red color and a layered structure. Starting from the third compartment, it shows large irregular nodular scale formation, the surface is composed of coarse particles, there are many pores, and the surface is dark red (or bright red) and white.

[0004] XRF chemical analysis of the scale shows that the main components are Al 2 O 3 , Fe 2 O 3 , SO 3 ; The sum of the three accounts for more than 75% of the total weight of the scale. Among them, Al 2 O 3 is mainly the part of the original ore that has not been leached. At the same time, ICP analysis is carried out on the red and white scale. The proportion of Fe element in the red scale is large, and the proportion of Al element in the white scale is large. XRD chemical analysis of the scale shows that the two main phases of the scale are red Fe 2 O 3 and white hydrated alunite (chemical formula: (H 3 O)Al 3 (SO 4 ) 2 (OH) 6 ).

[0005] According to the treated raw material laterite nickel ore, the main chemical reactions of Fe and Al elements during the high-pressure acid leaching process are as follows: Leaching of goethite: FeOOH + 3H + =Fe 3+ + 2H 2 O Hydrolysis of ferric sulfate at high temperature to form Fe 2 O 3 Precipitation: 2Fe 3+ +3H 2 O=Fe 2 O 3 ↓+6H + Hydrated alumina or Al 2 O 3 Is leached: AlOOH + 3H + =Al 3+ + 2H 2 O, Al 2 O 3 + 6H + =2Al 3+ + 3H 2 O Formation of hydrated alunite: 3Al 3+ + 2SO 4 2- +7H 2 O=(H 3 O)Al 3 (SO 4 ) 2 (OH) 6 ↓+ 5H + At present, the main means of cleaning the scale in the autoclave is through manual cleaning, which has a large labor intensity. At the same time, tools such as pneumatic picks and hammers used during the scale cleaning process are likely to damage the titanium materials inside the autoclave. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the present invention aims to provide a scale removal method for the HPAL process nickel leaching autoclave scale. By strictly controlling parameters such as the liquid caustic concentration, temperature, and time during the reaction process, after the alkali-soluble components in the structure are dissolved by the liquid caustic, the dense structure inside the scale is broken, making it loose and porous, and then it falls off from the inner wall of the autoclave under the stirring action. While ensuring the removal of the autoclave scale, corrosion of the titanium layer on the inner wall of the autoclave is avoided.

[0007] To achieve the above technical objectives, the present invention provides a method for removing scale from a nickel leaching autoclave in the HPAL process. The process is as follows: Liquid caustic soda is added to the nickel leaching autoclave to be descaled, and a high-temperature descaling reaction is carried out under stirring. After the reaction is completed, the residual caustic soda is discharged to obtain the product. The pH of the high-temperature descaling reaction is 13.5 - 14.

[0008] As a preferred solution, the conditions of the high-temperature descaling reaction are: the temperature is 120 - 180 °C, and the reaction time is 18 - 48 h.

[0009] In the present invention, the high-temperature descaling reaction must be strictly carried out according to the above requirements. If the temperature is too low, the reaction activity is too low, and even if the reaction time is extended, it is difficult to effectively remove scale. On the other hand, if the temperature is too high, on the one hand, it will lead to excessive heat energy consumption and a significant increase in cost. On the other hand, due to the increase in temperature, the pressure and alkali activity in the autoclave will also increase significantly, resulting in alkali corrosion of the inner wall of the autoclave.

[0010] As a preferred solution, the main components of the scale in the autoclave include: 30 - 35% hydrated alunite and 10 - 20% aluminum oxide.

[0011] As a preferred solution, the main reaction equation of the descaling reaction is: Equation 1: (H 3 O)Al 3 (SO 4 ) 2 (OH) 6 ↓ + 7NaOH = 3NaAlO 2 + 2Na 2 SO 4 + 8H 2 O; Equation 2: 2NaOH + H 2 O + Al 2 O 3 = 2Na[Al(OH) 4 ; As a preferred solution, the conditions of the high-temperature descaling reaction are: the temperature is 140 - 150 °C, and the reaction time is 20 - 30 h.

[0012] As a preferred solution, the preparation process of the liquid caustic soda in the descaling reaction is: industrial liquid caustic soda with a concentration of 30 - 50% is added to deionized water and stirred sufficiently to be diluted into liquid caustic soda with a concentration of 10 - 20%.

[0013] It should be noted that although theoretically, the higher the concentration of liquid caustic in the descaling reaction, the higher its reaction activity. However, in actual industrial production, too high a concentration of liquid caustic does not result in a higher descaling rate. This is because the scale in the nickel leaching autoclave does not consist entirely of alkali-soluble components. Alkali-soluble components such as aluminum salts and aluminum oxides only account for 50 - 70% of the scale. In the present invention, after dissolving the alkali-soluble components with liquid caustic, the dense structure inside the scale is disrupted, making it loose and porous, and then it falls off from the inner wall of the autoclave under the action of stirring. High-concentration alkali does not dissolve more scale components. On the contrary, high-concentration alkali not only causes more alkali waste but also corrodes the inner wall of the reaction kettle under high-temperature and high-pressure conditions. Therefore, the concentration of liquid caustic should be strictly in accordance with the above requirements.

[0014] As a preferred solution, the liquid level of the liquid caustic in the autoclave during the high-temperature descaling reaction is the same as the liquid level during nickel leaching production in the autoclave.

[0015] As a preferred solution, the rotation speed of stirring during the high-temperature descaling reaction is 60 - 100 rpm.

[0016] As a preferred solution, the recovered residual caustic is used as a neutralizing agent for neutralizing the HPAL process tailings.

[0017] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows: 1) The descaling method provided by the present invention strictly controls parameters such as the concentration, temperature, and time of the liquid caustic during the reaction process. After dissolving the alkali-soluble components in the structure with the liquid caustic, the dense structure inside the scale is disrupted, making it loose and porous, and then it falls off from the inner wall of the autoclave under the action of stirring. While ensuring the removal of the scale in the autoclave, it avoids corrosion of the titanium layer on the inner wall of the autoclave.

[0018] 2) The technical solution provided by the present invention has a simple process, is easy to operate, and can effectively solve the technical problem that the current descaling process overly relies on manual labor without the need to add additional equipment. After testing, when using the technical solution of the present invention for autoclave descaling, the descaling rate is above 95%, and the obtained alkali residue can be recycled as a neutralizing agent for neutralizing the HPAL process tailings. Detailed Embodiments

[0019] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and in detail in combination with embodiments. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] Example 1 Put 850 g of the scale deposit from Compartments 1 and 4 of the autoclave into a bench-scale autoclave, add liquid caustic soda with a concentration of 10%, heat up to 130 °C, keep warm and soak for reaction for 20 h. After completion, the remaining scale deposit is 42.5 g, and the scale removal rate is 95%. Observe that the colors of the inner wall of the autoclave, the coiled pipes and the titanium sheets have no change. The hardness test of the titanium sheets is normal, the weight has no change, and no corrosion is observed.

[0021] Example 2 Put 850 g of the scale deposit from Compartments 1 and 4 of the autoclave into a bench-scale autoclave, add liquid caustic soda with a concentration of 15%, heat up to 130 °C, keep warm and soak for reaction for 20 h. After completion, 17 g of the remaining scale deposit is not dissolved, and the scale removal rate is 98%. Observe that the colors of the inner wall of the autoclave, the coiled pipes and the titanium sheets have no change. The hardness test of the titanium sheets is normal, the weight has no change, and no corrosion is observed.

[0022] Example 3 Put 850 g of the scale deposit from Compartments 1 and 4 of the autoclave into a bench-scale autoclave, add liquid caustic soda with a concentration of 15%, heat up to 150 °C, keep warm and soak for reaction for 30 h. After completion, it can be seen that the scale deposit is 100% dissolved. Observe that the colors of the inner wall of the autoclave, the coiled pipes and the titanium sheets have no change. The hardness test of the titanium sheets is normal, the weight has no change, and no corrosion is observed.

[0023] Example 4 Put 850 g of the scale deposit from Compartments 1 and 4 of the autoclave into a bench-scale autoclave, add liquid caustic soda with a concentration of 20%, heat up to 130 °C, keep warm and soak for reaction for 30 h. After completion, the remaining scale deposit is 8 g, and the scale removal rate is 99%. Observe that the colors of the inner wall of the autoclave, the coiled pipes and the titanium sheets have no change. The hardness test of the titanium sheets is normal, the weight has no change, and no corrosion is observed.

[0024] Example 5 Put 850 g of the scale deposit from Compartments 1 and 4 of the autoclave into a bench-scale autoclave, add liquid caustic soda with a concentration of 20%, heat up to 140 °C, keep warm and soak for reaction for 30 h. After completion, the remaining scale deposit is 0, and the scale removal rate is 100%. Observe that the colors of the inner wall of the autoclave, the coiled pipes and the titanium sheets have no change. The hardness test of the titanium sheets is normal, the weight has no change, and no corrosion is observed.

[0025] Example 6 Put 850 g of the scale deposit from Compartments 1 and 4 of the autoclave into a bench-scale autoclave, add liquid caustic soda with a concentration of 20%, heat up to 130 °C, keep warm and soak for reaction for 48 h. After completion, the remaining scale deposit is 0 g, and the scale removal rate is 100%. Observe that the colors of the inner wall of the autoclave, the coiled pipes and the titanium sheets have no change. The hardness test of the titanium sheets is normal, the weight has no change, and no corrosion is observed.

[0026] Furthermore, the present invention also analyzed the residual caustic soda after dissolving the scale deposit in Example 5, and the results are shown in Table 1:

[0027] Example 7 After a high-pressure autoclave in a HPAL hydrometallurgical plant of a laterite nickel ore has operated for 7 months, the scale formation is about 130 t. Annual shutdown maintenance and cleaning of the scale in the high-pressure autoclave are started. According to the shutdown process, the high-pressure autoclave system is first replaced with clear water for cooling. When the temperature drops to about 90 °C, the replacement of clear water is stopped, and the liquid level in the high-pressure autoclave is maintained at the normal production level. At this time, the inside of the high-pressure autoclave is clear water. According to the actual water volume in each compartment of the autoclave, about 50 t of 48% liquid caustic soda is added, and the liquid caustic soda concentration in each compartment of the high-pressure autoclave is controlled at 15%. Then the temperature is raised to 140 °C, and stirring reaction is started for 24 h. After the reaction time ends, the temperature is continued to be lowered by replacing with clear water, and the residual alkali replaced is used as a tailing neutralizer. After the high-pressure autoclave is cooled, the manhole of the high-pressure autoclave is opened for inspection. It is found that most of the scale in the autoclave has been dissolved after checking the scale dissolution situation in the autoclave. There is still a small part of the dead zone in the high-pressure autoclave that needs to be manually cleaned. The scale amount manually cleaned is weighed by pumping and is about 5 t. The descaling rate is calculated to be 96%. This result proves that the method for dissolving the scale in the nickel leaching high-pressure autoclave of the HPAL process provided by the present invention meets the industrial use requirements.

Claims

1. A method for descaling nickel leaching autoclave in HPAL process, characterized in that: Liquid alkali is added into the nickel leaching autoclave to be descaled, and a high-temperature descaling reaction is carried out under stirring. After the reaction is completed, residual alkali is removed to obtain the product; the pH of the high-temperature descaling reaction is 13.5-14.

2. The method for descaling nickel leaching autoclave in HPAL process according to claim 1, characterized in that: The conditions of the high temperature descaling reaction are: temperature of 120-180° C., and reaction time of 18-48 hours.

3. The method for descaling nickel leaching autoclave in HPAL process according to claim 1, characterized in that: The main components of the autoclave scaling include: 30-35% hydrated alunite and 10-15% aluminum oxide.

4. The method for descaling nickel leaching autoclave in HPAL process according to claim 3, characterized in that: The main reaction equation of the descaling reaction is: Formula 1: (H3O)Al3(SO4)2(OH)6↓+ 7NaOH=3NaAlO2+2Na2SO4+8H2O; Formula 2: 2NaOH+ H2O+ Al2O3= 2Na[Al(OH)4].

5. The method for descaling nickel leaching autoclave in HPAL process according to claim 1, characterized in that: The conditions for the high-temperature descaling reaction are: a temperature of 140-150° C. and a reaction time of 20-30 hours.

6. The method for descaling nickel leaching autoclave in HPAL process according to claim 1, characterized in that: The preparation process of the liquid alkali in the descaling reaction is: adding industrial liquid alkali with a concentration of 30-50% into deionized water and fully stirring and diluting it into liquid alkali with a concentration of 10-20%.

7. The method for descaling nickel leaching autoclave in HPAL process according to claim 1, characterized in that: The liquid level of the liquid alkali in the autoclave during the high-temperature descaling reaction is the liquid level when the autoclave is performing nickel leaching production.

8. The method for descaling nickel leaching autoclave in HPAL process according to claim 1, characterized in that: The stirring speed during the high-temperature descaling reaction is 60-100 rpm.

9. The method for descaling nickel leaching autoclave in HPAL process according to claim 1, characterized in that: The residual alkali is recovered and used as a neutralizing agent for neutralizing the HPAL process tailings.

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