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9/30/93 <br />Responses to Comments <br />San Luis Reclamation Evaluation Report <br />Paqe 18 <br />Please comment on the accuracy of my understandings, and if <br />warranted, assure the Division that nitrates will not cause a <br />problem in the future from weathering of the tailings. <br />Response: The products of the oxidation of cyanide and <br />cyanide-bearing complexes using the copper <br />catalyzed, hydrogen peroxide process are cyanate, <br />water, metal hydroxide (solid phase), copper iron <br />cyanide complexes (solid phase), ammonia, calrbonate, <br />bicarbonate and, possibly, carbon dioxide. It is <br />normally the case that neither thiocyarlate nor <br />ammonia are removed in the process. Accordingly, <br />any oxidation of ammonia to nitrite and nitrate is <br />likely to be kinetically controlled with respect to <br />pH value and air contact. <br />At the pH of the San Luis tailings (pH of <br />approximately 7 to 8), such a process of ammonia <br />oxidation to nitrate would be expected to be slow. <br />Accordingly, if and where production of nitrate were <br />possible, the levels of nitrate are anticipated to <br />be low. we are including a copy of the publlication <br />"Chemistry and Treatment of Cyanidation Wastes" by <br />Dr. Adrian Smith and Dr. Terry Mudder. This <br />publication is considered to be the most up to date <br />publication on cyanide chemistry and treatment <br />methodologies. Please refer to Chapter 6 of this <br />publication for further information. <br />Comment: <br />Page 6, 3. With regard to the explanation of INCO chemistry <br />and with regard to comment 2 above, it appears that nitrates <br />may also be a product of the INCO process. <br />Please clarify the second equation shown in Figure 2.5; namely, <br />identify the composition of the fertilizer that is listed. <br />Also, please quantify the amount of nitrogenous fertilizer that <br />will be produced, and express that quantity in terms of its <br />pollution potential. <br />Response: In the INCO process, cyanide is oxidized by sulfur <br />dioxide and oxygen in the presence of copper to <br />cyanate. cyanate is hydrolyzed to form ammonia, <br />carbonate, bicarbonate and depending on pM value, <br />carbon dioxide. Metals species remaining in <br />solution are removed by hydrolysis and precipitation <br />as hydroxides. <br />