Some journals allow using citation (references) in the Conclusion part of a research paper. However, papers of most journals do not have citations in the Conclusion part, as that of the "Result" part of a paper.
When I do discussion and conclusions I use author for example:
In the line of the DL, the figure and role of the director does not disap
-
pear but emphasizes its central value, as it is considered a key piece
to develop a collective leadership, promoter of the improvement in
the learning (Spillane, 2017; Harris, 2012). It cannot underestimate
its importance, on the contrary it must be accepted from the role of
Impeller and coordinator of the improvement and innovation of the
processes of teaching-learning, since the research shows that without
(PDF) PERCEPTIONS OF SCHOOLS PRINCIPALS THROUGH DISTRIBUTED LEADERSHIP: CASE STUDY OF TWO PUBLIC SPANISH SCHOOLS. Available from: https://www.researchgate.net/publication/328702061_PERCEPTIONS_OF_SCHOOLS_PRINCIPALS_THROUGH_DISTRIBUTED_LEADERSHIP_CASE_STUDY_OF_TWO_PUBLIC_SPANISH_SCHOOLS [accessed Jan 25 2019].
As long as new ideas, which are not mentioned in the other parts of the article, are raised in the conclusion, I see no problem in the citation. Additionally, which ever parts of the article, I think that it is an obligation to cite ideas that do not belong to the article authors.
It is absolutely irrelevant. What conclusions are you drawing that do not derive from a discussion. the reference must already have been made in the discussion section, what's the point repeating it. Conclusion highlights the significant components or points raised in the discussion.
We usually do not use citations in conclusions. The purpose behind "conclusion" is to highlight the critical points driven in the discussion. Therefore, comparison of the research findings with those in the literature, justifying differences, and interpreting the findings in a meaningful way should have been completed in the discussion. It will be not logical and possibly raises questions if I see citations in the conclusion part.