| Nickeliferous laterite ore deposits are formed by the chemical weathering of nickeliferous peridotite rock under humid climates. The nickel content of ore is low, accounting for about 1%. Furthermore, through the weathering processes, the nickel is finally concentrated in different secondary minerals, which causes the difficulties of extracting nickel directly. At present, the typical methods for treating nickeliferous laterite ores including pyro-and hydrometallurgical processes only focus on the recovery of nickel, iron and cobalt, other substances as residue are discharged. The solid residuals not only take up a lot of land, and bring cause serious pollution to the environment. Therefore, in the long term it will be necessary to develop new and more economical process, and improve the high value-added green and comprehensive utilization of nickeliferous laterite ore.In this paper, a novel process for treating nickeliferous laterite ore is established. First, silicon from laterite-nickel ore is treated by sodium hydroxide, and then, magnesium is extracted from the desiliconization slag by carbonation, at last, nickel is recovered from carbide slag by leaching with ammonia carbonate, the remaining residue is used for a raw material for iron-making. The flow and the equipments of process are simple, so it is suitable for treating a variety of nickeliferous laterite ore.First of all, the process takes nickeliferous laterite ore as raw material and high concentration of sodium hydroxide or molten sodium hydroxide as the reaction media for preparing sodium silicate by the reaction of sodium hydroxide and silicon. After leaching and filtering, sodium silicate solution is obtained, and then silicon dioxide are prepared by twice carbonation of sodium silicate solution. According to the difference of reaction medium, the study on every procedure is as follows:1. The effects of stirring speed, leaching temperature, NaOH concentration, leaching time and liquid-to-ore mass ratio on the leaching ratio of SiO2 are investigated in the process of extracting silicon from nickeliferous laterite ore by leaching with high concentration sodium hydroxide. The orthogonal experiment based on single factor experiments is carried out for studying the optimum processing conditions, the optimum technology is established: leaching temperature 220℃, alkali concentration 85%, leaching time 90min, mass ratio of liquid to ore 5:1 and stirring speed 500r·min-1.The leaching ratio of SiO2 is over 85% under the optimum conditions, the elements of iron, magnesium and nickel are enriched in the residue, and the content of NiO is improved from 1.08% to 1.41%. The leaching kinetics of nickeliferous laterite ore in high concentration sodium hydroxide solution is investigated by the un-reaction shrinking core model, the results indicate that the leaching rate of SiO2 is controlled by the diffusion through the product layer. The apparent activation energy is calculated to be 10.56 kJ·mol-1 and the kinetics model can be expressed as: 1-3(1-α)1/3+2(1-α)=69.41 exp(-10560/RT) t.2. The effects of reaction temperature, reaction time, alkali-to-ore mass ratio and stirring speed on the extraction of SiO2 are investigated in the process of extracting silicon from nickeliferous laterite ore by molten sodium hydroxide. The orthogonal experiment based on single factor experiments is carried out for studying the optimum processing conditions, the optimum technology is established:reaction temperature 550℃, reaction time 90min, mass ratio of alkali to ore 4.5:1 and stirring speed 400r·min-1.The leaching ratio of SiO2 is over 93% under the optimum conditions, the elements of iron, magnesium and nickel are enriched in the residue, and the content of NiO is improved from 1.08% to 1.62%. The leaching kinetics of nickeliferous laterite ore in molten sodium hydroxide is investigated by the un-reaction shrinking core model, the results indicate that the process of extracting SiO2 is controlled by the chemical reaction. The apparent activation energy is calculated to be 44.01 kJ·mol-1, the kinetics model can be expressed as:1-(1-α)1/3=17.67 exp(-44010/RT) t.3. The sodium silicate solution is processed by twice carbonation, the relationships of reaction time and reaction rate, pH of the solution are studied. The results show that the pH end point for first carbonation is 11, the pH end point for second carbonation is 9. The effects of reaction temperature, sodium silicate concentration, CO2 gas flow rate and the modules of sodium silicate on the configuration of SiO2 product are investigated. The conditions for preparing SiO2 are:reaction temperature 60～80℃, sodium silicate concentration <90g·L CO2 gas flow rate 20～30ml·min-1, the modules of sodium silicate< 1. The SiO2 product is amorphous and the purity is 99.93%.4. The sodium carbonate solution is processed by caustification, the effects of reaction temperature, sodium carbonate concentration, reaction time and the mol ratio of CaO to Na2CO3 on causticization rate are investigated. The orthogonal experiment based on single factor experiments is carried out for studying the optimum processing conditions, the optimum technology is established:reaction temperature 85℃, reaction time is 8min, sodium carbonate concentration 100g·L-1, the mol ratio of CaO to Na2CO3 1.2:1.Thc causticization rate of sodium carbonate solution is over 92%.Secondly, the desiliconization slag of nickeliferous laterite ore is treated by carbonization leaching, the reaction between magnesium hydroxide and CO2 occurs, the magnesium bicarbonate solution obtained decomposes by heacting for producing magnesium carbonate. Magnesium oxide is prepared by sintering magnesium carbonate. The effects of stirring speed, leaching temperature, leaching time and liquild-to-solid ratio on the extraction ratio of MgO are studied in the process of extracting magnesium from desiliconization slag of nickeliferous laterite ore by carbonization leaching. The orthogonal experiment based on single factor experiments is carried out for studying the optimum processing conditions, the optimum technology is established:stirring speed 600 r·min-1, reaction temperature 15℃, reaction time 36h and liquid-to-solid ratio 50:1, the extraction ratio of MgO can be raised as high as 92%, the elements of iron and nickel are enriched further, and the content of NiO is improved from 1.41% to 2.96%. The leaching kinetics of desiliconization slag is investigated by the un-reaction shrinking core model, the results indicate that the process of extracting MgO is controlled by the chemical reaction. The apparent activation energy of the leaching process is found to be 20.45 kJ·mol-1, and the kinetics model can be expressed as: 1-(1-α)1/3=3.24×1O5 exp(-20450/RT) t. The purity of MgO product prepared is 92.6%, reaching the technical specification of Industrial-grade magnesium oxide:HG/T2573-94.Finally, ammonium carbonate solution is used for leaching slag carbonation. Basic nickel carbonate is obtained after ammonia still process of nickel-ammonia complex solution, the nickel oxide can be obtained by calcining basic nickel carbonate. The effects of stirring speed, leaching temperature, leaching time, ammonium carbonate concentration and liquild-to-solid ratio on the recovery of NiO are investigated in the process of extracting nickel from carbide slag by ammonia carbonate leaching. The orthogonal experiment based on single factor experiments is carried out for studying the optimum processing conditions, the optimum technology is established:stirring speed 250r·min-1, leaching temperature 60℃leaching time 150min, ammonium carbonate concentration 6mol·L-1 and liquid-to-solid ratio 5:1, the recovery of NiO can be over 92%, the remaining residue is used for a raw material for iron-making or high-added value utilization. The leaching kinetics of carbide slag is investigated by the un-reaction shrinking core model, the results indicate that the process of extracting MgO is controlled by the chemical reaction. The apparent activation energy of the leaching process is found to be 27.49 kJ·mol-1, and the kinetics model can be expressed as: 1-(1-α)1/3=83.10 exp(-27490/RT) t. The Ni content of NiO product prepared is 75.47%, reaching the technical specification of second-grade nickel oxide:GB8633-88.Economic analysis and environmental assessment is carried out by calculating materiel equation and energy equation. We can know:This technology’ synthetical benefit of economy and environment is better, the high-added value and comprehensive utilization of nickeliferous laterite ore is achieved, chemical raw materials are recycled, no contamination is charged. Therefore, this process is a "grassy" technology having good social benefit. |
PDF Full Text Request