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W501 – INTERNATIONAL MODULE: MEASUREMENT OF HAZARDOUS SUBSTANCES INCLUDING RISK ASSESSMENT

W501 –国际模块：有害物质测量，包括风险评估

CASE STUDY 3 - SUPPLEMENTARY INFORMATION FOR COURSE PRESENTER

实例研究3 - 课程主讲所需补充信息

As with all case studies the aim is to reinforce the knowledge previously transmitted in lectures by application of those learnings to a practical situation.
As described in the Teaching Guide, students should break into their groups and use the information provided to undertake the required tasks.
As gold extraction may be an unfamiliar process to many students, a short overview of the process using the supplementary information in the case study should be provided.
Students should be challenged with the question: If you were the hygienist asked to assess this situation how would you go about that process?
There are two parts to the process that students are being asked to consider. These are:
a) The transportation of crushed ore including the extraction of gold, using added chemicals (photographs1 & 2).
b) The smelting of impure gold following electrolysis (photograph3).
Key points that students should note as part of their initial appraisal are:
a) Extraction Process
· Transportation of the crushed ore via conveyor does not produce significant dust levels due to the ore being wet (photograph1).
· Addition of the hydrated lime does give rise to significant levels of dust (fine hydrated lime) as can be observed in photograph2.
· The person adding the hydrated lime appears to be wearing respiratory protection and a raincoat so as to protect themselves from exposure to the corrosive dust.
While not part of this course it may be useful to point out that the use of an impervious plastic raincoat in this manner in a tropic West African climate could give rise to other issues such as heat stress.
· Maintenance of pH levels is critical so as to minimise the evolution of hydrogen cyanide.
b) Smelting Process
· The smelting process can release other metals such as mercury as a vapour.
· The extraction system is not well maintained thus reducing the capture velocity of the hood.
· As the extraction system is inefficient, not only is there potential for the metal impurities in the gold that are liberated as a vapour (egmercury) to build up, but also the combustion gases of the furnace (egcarbon monoxide).
· Heat may also be a problem as radiant heat from the furnace.
Students should be encouraged to use the material in Section5 of the manual to assist them in designing their surveys and presentation. / 与所有实例研究相同，本实例研究旨在通过理论联系实践，强化课堂传授知识。
按照教学指南中的规定，将学员分为若干小组，且要求学员使用可用信息完成相关任务。
因为大多数学员对提金工艺不熟，所以，应在实例研究中采用补充信息方式简要描述工艺。
学员应回答如下问题：假设学员自己为必须评估该种情况的卫生员，请描述如何完成该种评估？
对于该工艺，学生应注意如下两点：
a) 碎矿石的运输，包括采用添加化学品方式提金（照片1和2） 。
b) 电解后对不纯黄金进行熔炼（照片3 ）。
学员在初始评估中必须关注的要点如下：
a) 提取工艺
· 因矿石潮湿，采用输送机运输碎矿石不会产生大量的粉尘（照片1）。
· 添加熟石灰会导致产生大量粉尘（较细熟石灰），详见照片2。
· 添加熟石灰的作业人员佩戴呼吸防护装置和雨衣，以避免接触腐蚀性粉尘。
必须指出得是，在热带西非气候区域使用不透水的塑料雨衣可能会导致出现其它问题，如热应激。
· 保持pH数值不变非常关键，可以尽量减少氰化氢的挥发。
b) 冶炼工艺
· 冶炼工艺可释放其它金属，如汞蒸汽。
· 如提金系统维护不善，会减少机罩的捕获速度。
· 如提金系统的效率不高，可能会导致黄金中不存金属以蒸汽（如汞）形式释放，也可能导致熔炉中产生燃烧气体（如一氧化碳）。
· 因熔炉中可能会有辐射热，所以热量也可能会是问题。
教师应鼓励学员使用本手册中第5节内容来设计其调查和简报说明。