The analysis of phosphate, a common undergraduate teaching laboratory, produces waste containing molybdenum blue. See equations 1 and 2 that show the reaction between molybdate and phosphate with stannous chloride as the reductant, resulting in the formation of the molybdenum blue compound. According to various safety data sheets, molybdenum (Mo) and tin (Sn) are considered to be hazardous to the environment. The current standard procedure for the removal of Mo is to increase the pH of the waste with NaOH and precipitate with CaCl2. This research proposes that it would be beneficial to increase the pH with Na2CO3 in order to precipitate molybdenum-containing anions as calcium salts and Sn(II) and Sn(IV) cations as carbonate salts (equations 3-6). Atomic Absorption Spectroscopy results will be presented to determine the effectiveness of the proposed waste removal procedure. While this treatment will be beneficial to the environment, it would be beneficial to the education of students as well. The improved procedure is proposed as a teaching lab, in which students treat their own waste prior to waste disposal, thereby giving students important experience with and understanding of the treatment/disposal of hazardous waste. (1) PO43- + 12MoO42- + 27H+ --&gt; H3PO4(MoO3)12 + 12H2O (2) H3PMo(VI)12O40 + Sn2+ --&gt; [H4PMo(VI)8Mo(V)4O40]3- + Sn4+ (molybdenum blue) (3) Ca2+(aq) + MoO42-(aq) --&gt; CaMoO4(s) (4) 3Ca2+(aq) + 2[H4PMo(VI)8Mo(V)4O40]3-(aq) --&gt; Ca3(H4PMo(VI)8Mo(V)4O40)2(s) (5) Sn2+(aq) + CO32-(aq) --&gt; SnCO3(s) (6) Sn4+(aq) + 2CO32-(aq) --&gt; Sn(CO3)2(s)

Proposed teaching lab and improved procedure for the removal of molybdenum and sin from waste generated by the quantitative analysis of phosphate: Verification by atomic absorption spectroscopy

255th National Meeting (2018)

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