Development of Effective Extraction Process of Insoluble Sb Species in Urban Mine By Controlling the Metal Complexes Condition - Relationship Between the Local Structure of Sb in Urban Mine and the Condition of Sb Complexes in Sb-Tartaric Acid-OH Aqueous System -
Authors: Takahashi Hideyuki , Ueno Shunya , Yokoyama Shun , Tohji Kazuyuki 
Published: February 2020

It is well known that some of rare metal, has accumulated as ‘urban mine’ without effective utilization. Among these rare metals, a part of antimony (Sb) cannot be recycled because of its inseparability and insolubility, nevertheless Sb-rich slag, one of smelting residues, includes about over few ten wt% of antimony (Sb). On the other hand, we reported the new synthesis method of well crystallized and uniform alloy nanoparticles by controlling the homogenization of metallic complexes in the aqueous solution. In this method, metal complex condition is calculated by using critical stability constants as a function of solution pH. Taking the fact that this calculation results involve the relationship between metal complex condition and solution condition into consideration, it expected that this calculation method can be applied to development the new Sb extraction process. Therefore, in this study, relationship between the condition of Sb in insoluble urban mine and metal complexes condition in aqueous solution was evaluated.
Cu slag was selected as the target sample, since it contained the insoluble Sb against to which hard to recycle by traditional acid extraction method. Cl and also tartaric acid was used as a complexing reagents. Appropriate aqueous solution condition, which Sb exists as soluble complexes, was predicted by using complex concentration calculation method. Soluble species were analyzed by using ESI-TOF-MS (Electro Spray Ionization Time of Fright Mass Spectroscopy). Condition of these soluble species and also insoluble species were analyzed by EXAFS and XANES, XPS.
At a first step, simple Sb3+-Cl--OH- complex system was selected. Results of calculation indicated that complex species change from Sb-Cl complex system to Sb-OH complex system at around pH 2. This results expect that Sb dissolution system is dramatically changed at around this pH range. Therefore, we demonstrated a dissolution test of Sb in Cu slag by utilizing Cl-OH aqueous solution. ICP data showed that dissolved amount of Sb become minimum value in pH 2~3, which showed good correspond with the calculation results. Since Sb-OH complexes identified by ESI-TOF-MS mostly consisted of Sb5+ ion, Sb in solution was oxidized to be soluble complex with charge of 5+, rather than the formation of precipitable Sb (III) hydroxide. This increase dissolution amount of Sb at high pH range. The insoluble materials after dissolution treatments mentioned above were also analyzed by XPS. As the results, it confirmed that binding energy of Sb decreased with increasing the treatment pH. This means that Sb (V) compounds, which known as insoluble form, could be soluble at high pH ranges.
As mentioned above, insoluble Sb can be extracted from urban mine, nevertheless extracted amount of Sb was not high in this system, since stability constants and also solubility of Sb-Cl and/or Sb-OH complex was low. Therefore, at the next step, tartaric acid was selected as a new ligand, because of it’s high stability constant with Sb. Calculation results of Sb-C4O6H4
2--OH- system clearly demonstrated that Sb species can restrict to only one complex, [Sb3+
2(C4O6H4
2-)2]2+, under pH 6. Solubility of this chelate complex is expected to high, so, leaching tests of Sb-rich slag was performed. As a results, dissolution ratio of Sb reached to 70% (15000ppm) of Sb in the slag at pH 2.1. These results means that this calculation method will provide one of the solution for new recovery process of rare metals in urban mine. Another result, such as EXAFS and XANES, will be presented in our session. This work has been supported by the JOGMEC.