基于热力学分析与响应曲面法研究磷尾矿中钙镁浸出率

在回收磷尾矿中钙镁资源时,通常先将尾矿进行煅烧,然后利用浸取工艺浸取尾矿中的钙镁,用于后续资源回收。在煅烧过程中需要让磷尾矿中的白云石尽量分解,而氟磷灰石得到保留。研究利用HSC Chemistry软件进行磷尾矿煅烧热力学分析优化煅烧条件,在尾矿煅烧物浸取钙镁过程中,基于响应曲面法,分析铵钙物质的量比(7∶1~11∶1)、液固质量比(7∶1~9∶1)、反应温度(60~80℃)、反应时间(50~70 min)的交互作用对钙镁浸出率的影响,对钙镁浸出条件进行优化。结果表明,白云石完全分解为CaO、MgO且氟磷灰石不分解的煅烧温度范围为(900~1200℃)。优化钙镁浸出条件:铵钙比物质的量比为10∶1、液固质量比为8∶1、反应温度为71℃、反应时间66 min时获得最佳钙镁的浸出率,分别为92.25%和86.19%。依据优化后的浸出条件,进行多次实验,实验结果为钙浸出率为91.95%、镁浸出率为85.85%。实验结果与优化结果较为接近,证明优化结果较为准确,且通过模拟优化及实验验证,可以看出铵钙比对浸出率的影响较大。

废弃镁-铬耐火材料中镁的浸出动力学

本研究采用SEM-EDS和BSE对废弃镁-铬耐火材料浸出前后的微观特性进行了检测,通过浸出动力学试验研究了浸出条件对镁浸出的影响,采用统计和作图法对镁的浸出过程进行了动力学分析。结果表明,原料中不同物相之间嵌布关系复杂,浸出渣为铬铁尖晶石且颗粒中存在各种孔洞和裂纹。升高温度、增加盐酸浓度和液固比可以加快镁的浸出速度,从而促进整个浸出过程,其中温度的促进作用最强。最终确定废弃镁-铬耐火材料中镁的浸出过程符合渐进转化模型,其控制步骤为化学反应,表观活化能为69.11 kJ/mol,动力学方程为:X/(1-X)=4.898×10^(8)×CHCl0.7982×(L/S)0.7407×e-8312/T×t0.9276。

污泥4种热处理产物中磷的化学提取-沉淀回收性能

污水处理厂污泥中磷含量较高,对磷进行回收能有效实现磷资源的二次利用。采用磷酸铵镁(MAP)回收法分别对污泥4种热处理产物阴燃灰、掺烧灰、焚烧灰和热解焦的酸浸出液进行磷回收试验,重点分析了各热处理产物在酸浸出-MAP路线下的磷回收性能,包括磷沉淀率、产物中磷和杂质含量,并进一步探究了沉淀产物的环境安全性。结果表明,通过酸浸出-MAP回收法,单位质量沉淀产物磷质量分数达19.82~31.71 mg/g,原污泥中磷回收率达49.25%~65.81%。磷回收性能由高到低依次为焚烧灰、热解焦、阴燃灰、掺烧灰。酸浸出-MAP回收产物中含有大量Ca、Fe、Al和Si杂质,且含有一定量Zn、Pb、Cr、Cu、Cd、As和Ni,其中Zn含量远高于其他重金属含量。产物纯度和环境安全性由高到低依次为焚烧灰、掺烧灰、热解焦、阴燃灰。在沉淀产物的环境安全性方面,阴燃灰、焚烧灰和热解焦的酸浸出-MAP回收产物中重金属含量均符合GB/T 23349—2009《肥料中砷、镉、铅、汞生态指标》和GB 4284—2018《农用污泥污染物控制标准》。掺烧灰的酸浸出-MAP回收产物中Cd质量分数为3.20 mg/kg,超过农用污泥污染物控制标准限值3.00 mg/kg。

Removal of magnesium and calcium from electric furnace titanium slag by H_3PO_4 oxidation roasting-leaching process

H3PO4 oxidation roasting followed by HCl acid leaching was proposed to remove magnesium and calcium from electric furnace titanium slag containing 3.12% MgO and 0.86% CaO. XRF, XRD and SEM techniques were used to characterize the composition, mineral phase component and microstructure of the titanium slag. The H3PO4 oxidation thermodynamic, mineral phase transformation, microstructure, element distribution in titanium slag during H3PO4 oxidation process and leaching process were investigated. The thermodynamic analysis indicated that H3PO4 could promote the decomposition of MgTi2O5 and CaSiO3. The results indicated that H3PO4 could effectively promote the transformation of titanium-bearing mineral to rutile and enrich the impurities in MxTi（3-x）O5 into phosphate which could be removed by acid leaching process. Under the studied conditions, the leaching rates of magnesium and calcium reached 94.68% and 87.19%, respectively. The acid leached slag containing 0.19% MgO and 0.13% CaO（mass fraction） was obtained.

Leaching kinetics of low-grade copper ore containing calcium-magnesium carbonate in ammonia-ammonium sulfate solution with persulfate

The leaching kinetics of copper from low-grade copper ore was investigated in ammonia-ammonium sulfate solution with sodium persulfate. The effect parameters of stirring speed, temperature, particle size, concentrations of ammonia, ammonium sulfate and sodium persulfate were determined. The results show that the leaching rate is nearly independent of agitation above 300 r/min and increases with the increase of temperature, concentrations of ammonia, ammonium sulfate and sodium persulfate. The EDS analysis and phase quantitative analysis of the residues indicate that bornite can be dissolved by persulfate oxidization. The leaching kinetics with activation energy of 22.91 kJ/mol was analyzed by using a new shrinking core model （SCM） in which both the interfacial transfer and diffusion across the product layer affect the leaching rate. A semi-empirical rate equation was obtained to describe the leaching process and the empirical reaction orders with respect to the concentrations of ammonia, ammonium sulfate and sodium persulfate are 0.5, 1.2 and 0.5, respectively.

Application of response surface methodology in optimization of bioleaching parameters for high-magnesium nickel sulfide ore

The response surface methodology(RSM)was used to optimize the operating parameters during the bioleaching of Jinchuan high-magnesium nickel sulfide ore.The particle size,acid addition,pulp density and inoculation amount were chosen as the investigated parameters.To maximize the leaching efficiency of nickel,copper,cobalt and minimize the dissolution of magnesium and iron ions,the model suggested a combination of optimal parameters of particles less than 0.074 mm being 72.11%,sulfuric acid addition being 300 kg/t,pulp density being 5%and inoculation amount being 12.88%.Under the conditions,the average results of three parallel experiments were 89.43%of nickel leaching efficiency,36.78%of copper leaching efficiency,84.07%of cobalt leaching efficiency,49.19%of magnesium leaching efficiency and 0.20 g/L of iron concentration.The model indicated that the most significant factor in response of the leaching efficiency of valuable metal is the particle size,and the most significant factor in response to the leaching efficiency of harmful ions(Mg2+)is the amount of sulfuric acid addition.And according to the suggested models,no significance of the interaction effect between particle size and acid addition was shown.Under the optimized parameters suggested by models,the valuable metals could be separated from harmful ions during the bioleaching process.

Stepwise recovery of magnesium from low-grade ludwigite ore based on innovative and clean technological route

A novel and clean technological route for the comprehensive utilization of low-grade ludwigite ore was proposed, inwhich magnesium was extracted by metallizing reduction？magnetic separation, sulfuric acid leaching and ethanol precipitationoperation. Meanwhile, iron-rich product, silicon-rich product and boron-rich product were obtained, respectively. In the process ofmetallizing reduction-magnetic separation, 94.6% of magnesium was enriched in the non-magnetic substance from the ore reducedat 1250 ℃ for 60 min with the ore size of 0.50-2.00 mm and coal size of 0.50-1.50 mm. When the non-magnetic substance wasleached at 90 ℃ for 15 min with the liquid-to-solid ratio of 7：1, 87.4% of magnesium was leached into the liquor separated fromsilicon gathering in leaching residue. The ethanol precipitation was conducted for 30 min with the ethanol-to-original liquid volumeratio of 1.5：1 at room temperature. 97.2% of magnesium was precipitated out with the initial concentration of 0.8 mol/L in the formof MgSO4·7H2O.